This is a good question, quite a lot of code is going to need to be updated for this aspect of Swift 6 and it's not as simple as just adding any as you would be missing out on the subtle advantages of using some, opaque types.
There is, just enough information available using SourceKit to to identify where protocols are being referenced in source so I've written a small Swift "script" to attempt to help automate this conversion.
It follows the following:
There are a few extra edge cases handled using regular expressions and system protocol references are always elided to any to avoid breaking conformances. The script follows up by using the compiler with option -enable-upcoming-feature ExistentialAny to pick up any remaining missing anys and patches them in.
There will always be a few remaining errors to fix manually but it's working reasonably well. The results so far compiling the most popular Swift packages showing the deduplicated number of compilation errors compiling for option ExistentialAny before and after running the script are below.
repos/<rank>_<stars>_<name> ... #errors
repos/0001_37713_Alamofire/AFTER.txt 10
repos/0001_37713_Alamofire/BEFORE.txt 363
repos/0002_35061_fastlane/AFTER.txt 7
repos/0002_35061_fastlane/BEFORE.txt 7
repos/0003_25532_Charts/AFTER.txt 52
repos/0003_25532_Charts/BEFORE.txt 199
repos/0004_24159_SDWebImage/AFTER.txt 0
repos/0004_24159_SDWebImage/BEFORE.txt 0
repos/0005_22763_lottie-ios/BEFORE.txt 0
repos/0006_22232_RxSwift/AFTER.txt 26
repos/0006_22232_RxSwift/BEFORE.txt 761
repos/0007_21791_vapor/AFTER.txt 2
repos/0007_21791_vapor/BEFORE.txt 2
repos/0008_21366_SwiftyJSON/AFTER.txt 3
repos/0008_21366_SwiftyJSON/BEFORE.txt 8
repos/0009_20837_Hero/AFTER.txt 0
repos/0009_20837_Hero/BEFORE.txt 0
repos/0010_20172_Kingfisher/AFTER.txt 18
repos/0010_20172_Kingfisher/BEFORE.txt 109
repos/0011_18528_SnapKit/AFTER.txt 0
repos/0011_18528_SnapKit/BEFORE.txt 39
repos/0012_16168_SwiftLint/BEFORE.txt 0
repos/0013_15620_IQKeyboardManager/AFTER.txt 3
repos/0013_15620_IQKeyboardManager/BEFORE.txt 3
repos/0014_15353_realm-swift/AFTER.txt 17
repos/0014_15353_realm-swift/BEFORE.txt 235
repos/0015_14594_carthage/AFTER.txt 2
repos/0015_14594_carthage/BEFORE.txt 2
repos/0016_13989_Moya/AFTER.txt 62
repos/0016_13989_Moya/BEFORE.txt 62
repos/0017_13873_perfect/AFTER.txt 0
repos/0017_13873_perfect/BEFORE.txt 9
repos/0018_13854_PromiseKit/AFTER.txt 0
repos/0018_13854_PromiseKit/BEFORE.txt 24
repos/0019_13694_fmdb/AFTER.txt 0
repos/0019_13694_fmdb/BEFORE.txt 0
repos/0020_12703_CocoaLumberjack/AFTER.txt 2
repos/0020_12703_CocoaLumberjack/BEFORE.txt 2
repos/0021_12409_IGListKit/AFTER.txt 4
repos/0021_12409_IGListKit/BEFORE.txt 3
repos/0022_12209_CocoaAsyncSocket/AFTER.txt 0
repos/0022_12209_CocoaAsyncSocket/BEFORE.txt 0
repos/0023_11443_Eureka/AFTER.txt 3
repos/0023_11443_Eureka/BEFORE.txt 3
repos/0024_11225_SkeletonView/AFTER.txt 3
repos/0024_11225_SkeletonView/BEFORE.txt 3
repos/0025_11197_SwifterSwift/AFTER.txt 3
repos/0025_11197_SwifterSwift/BEFORE.txt 10
repos/0026_10141_NVActivityIndicatorView/AFTER.txt 0
repos/0026_10141_NVActivityIndicatorView/BEFORE.txt 0
repos/0027_9447_Quick/AFTER.txt 0
repos/0027_9447_Quick/BEFORE.txt 5
repos/0028_9173_AudioKit/AFTER.txt 0
repos/0028_9173_AudioKit/BEFORE.txt 150
repos/0029_9100_CryptoSwift/AFTER.txt 16
repos/0029_9100_CryptoSwift/BEFORE.txt 65
repos/0030_8962_ObjectMapper/AFTER.txt 0
repos/0030_8962_ObjectMapper/BEFORE.txt 20
repos/0031_8800_swift-package-manager/AFTER.txt 1
repos/0031_8800_swift-package-manager/BEFORE.txt 1
repos/0032_8687_R.swift/AFTER.txt 2
repos/0032_8687_R.swift/BEFORE.txt 2
repos/0033_8620_IBAnimatable/AFTER.txt 3
repos/0033_8620_IBAnimatable/BEFORE.txt 3
repos/0034_8286_SQLite.swift/AFTER.txt 40
repos/0034_8286_SQLite.swift/BEFORE.txt 265
repos/0035_7972_swiftgen/AFTER.txt 10
repos/0035_7972_swiftgen/BEFORE.txt 10
repos/0036_7611_Reachability.swift/AFTER.txt 0
repos/0036_7611_Reachability.swift/BEFORE.txt 0
repos/0037_7572_PureLayout/AFTER.txt 0
repos/0037_7572_PureLayout/BEFORE.txt 0
repos/0038_7529_Kitura/AFTER.txt 2
repos/0038_7529_Kitura/BEFORE.txt 2
repos/0039_7332_Starscream/AFTER.txt 0
repos/0039_7332_Starscream/BEFORE.txt 69
repos/0040_7295_Cartography/AFTER.txt 19
repos/0040_7295_Cartography/BEFORE.txt 104
repos/0041_7206_ReSwift/AFTER.txt 7
repos/0041_7206_ReSwift/BEFORE.txt 14
repos/0042_7187_JTAppleCalendar/AFTER.txt 3
repos/0042_7187_JTAppleCalendar/BEFORE.txt 3
repos/0043_7150_JVFloatLabeledTextField/AFTER.txt 2
repos/0043_7150_JVFloatLabeledTextField/BEFORE.txt 2
repos/0044_7087_facebook-ios-sdk/BEFORE.txt 0
repos/0045_7001_swift-nio/AFTER.txt 2
repos/0045_7001_swift-nio/BEFORE.txt 2
repos/0046_6939_RIBs/AFTER.txt 14
repos/0046_6939_RIBs/BEFORE.txt 14
repos/0047_6932_SwiftDate/AFTER.txt 31
repos/0047_6932_SwiftDate/BEFORE.txt 96
repos/0048_6922_KeychainAccess/AFTER.txt 0
repos/0048_6922_KeychainAccess/BEFORE.txt 5
repos/0049_6745_ViewAnimator/AFTER.txt 3
repos/0049_6745_ViewAnimator/BEFORE.txt 3
repos/0050_6703_Nuke/AFTER.txt 40
repos/0050_6703_Nuke/BEFORE.txt 113
repos/0051_6624_sourcery/AFTER.txt 2
repos/0051_6624_sourcery/BEFORE.txt 2
repos/0052_6545_SwiftMessages/AFTER.txt 3
repos/0052_6545_SwiftMessages/BEFORE.txt 3
repos/0053_6505_FSPagerView/AFTER.txt 3
repos/0053_6505_FSPagerView/BEFORE.txt 3
repos/0054_6300_swift-composable-architecture/AFTER.txt 2
repos/0054_6300_swift-composable-architecture/BEFORE.txt 2
repos/0055_6209_DTCoreText/AFTER.txt 1
repos/0055_6209_DTCoreText/BEFORE.txt 1
repos/0056_6117_KIF/AFTER.txt 4
repos/0056_6117_KIF/BEFORE.txt 4
repos/0057_6075_AMScrollingNavbar/AFTER.txt 3
repos/0057_6075_AMScrollingNavbar/BEFORE.txt 3
repos/0058_5992_SwiftyStoreKit/AFTER.txt 6
repos/0058_5992_SwiftyStoreKit/BEFORE.txt 56
repos/0059_5915_Sparkle/BEFORE.txt 0
repos/0060_5877_SwiftEntryKit/AFTER.txt 3
repos/0060_5877_SwiftEntryKit/BEFORE.txt 3
repos/0061_5851_swipecellkit/AFTER.txt 3
repos/0061_5851_swipecellkit/BEFORE.txt 3
repos/0062_5839_macaw/AFTER.txt 2
repos/0062_5839_macaw/BEFORE.txt 2
repos/0063_5763_SwiftFormat/AFTER.txt 0
repos/0063_5763_SwiftFormat/BEFORE.txt 19
repos/0064_5506_SwiftyBeaver/AFTER.txt 0
repos/0064_5506_SwiftyBeaver/BEFORE.txt 30
repos/0065_5481_XcodeGen/AFTER.txt 10
repos/0065_5481_XcodeGen/BEFORE.txt 10
repos/0066_5354_SideMenu/AFTER.txt 3
repos/0066_5354_SideMenu/BEFORE.txt 3
repos/0067_5298_Swinject/AFTER.txt 5
repos/0067_5298_Swinject/BEFORE.txt 76
repos/0068_5191_MessageKit/BEFORE.txt 0
repos/0069_5150_GRDB.swift/AFTER.txt 15
repos/0069_5150_GRDB.swift/BEFORE.txt 112
repos/0070_4997_Surge/AFTER.txt 0
repos/0070_4997_Surge/BEFORE.txt 0
repos/0071_4949_FloatingPanel/AFTER.txt 3
repos/0071_4949_FloatingPanel/BEFORE.txt 3
repos/0072_4941_PermissionsKit/AFTER.txt 3
repos/0072_4941_PermissionsKit/BEFORE.txt 3
repos/0073_4891_OHHTTPStubs/AFTER.txt 0
repos/0073_4891_OHHTTPStubs/BEFORE.txt 3
repos/0074_4862_Instructions/AFTER.txt 3
repos/0074_4862_Instructions/BEFORE.txt 3
repos/0075_4802_socket.io-client-swift/AFTER.txt 3
repos/0075_4802_socket.io-client-swift/BEFORE.txt 3
repos/0076_4744_gpuimage2/AFTER.txt 0
repos/0076_4744_gpuimage2/BEFORE.txt 29
repos/0077_4742_ESTabBarController/AFTER.txt 3
repos/0077_4742_ESTabBarController/BEFORE.txt 3
repos/0078_4726_SwiftUIX/AFTER.txt 101
repos/0078_4726_SwiftUIX/BEFORE.txt 101
repos/0079_4648_SwiftyUserDefaults/AFTER.txt 0
repos/0079_4648_SwiftyUserDefaults/BEFORE.txt 7
repos/0080_4617_async/AFTER.txt 0
repos/0080_4617_async/BEFORE.txt 0
repos/0081_4542_PhoneNumberKit/AFTER.txt 0
repos/0081_4542_PhoneNumberKit/BEFORE.txt 7
repos/0082_4462_Advance/AFTER.txt 0
repos/0082_4462_Advance/BEFORE.txt 0
repos/0083_4451_Nimble/AFTER.txt 21
repos/0083_4451_Nimble/BEFORE.txt 84
repos/0084_4405_AnimatedCollectionViewLayout/AFTER.txt 3
repos/0084_4405_AnimatedCollectionViewLayout/BEFORE.txt 3
repos/0085_4382_chartview/AFTER.txt 3
repos/0085_4382_chartview/BEFORE.txt 3
repos/0086_4381_swift-algorithms/AFTER.txt 0
repos/0086_4381_swift-algorithms/BEFORE.txt 0
repos/0087_4215_EFQRCode/AFTER.txt 0
repos/0087_4215_EFQRCode/BEFORE.txt 7
repos/0088_4212_bond/AFTER.txt 2
repos/0088_4212_bond/BEFORE.txt 2
repos/0089_4188_SVGKit/AFTER.txt 8
repos/0089_4188_SVGKit/BEFORE.txt 8
repos/0090_4101_Bagel/AFTER.txt 1
repos/0090_4101_Bagel/BEFORE.txt 1
repos/0091_4089_ActiveLabel.swift/AFTER.txt 3
repos/0091_4089_ActiveLabel.swift/BEFORE.txt 3
repos/0092_4019_Publish/AFTER.txt 2
repos/0092_4019_Publish/BEFORE.txt 2
repos/0093_3984_Siren/AFTER.txt 3
repos/0093_3984_Siren/BEFORE.txt 3
repos/0094_3959_SkyFloatingLabelTextField/AFTER.txt 3
repos/0094_3959_SkyFloatingLabelTextField/BEFORE.txt 3
repos/0095_3880_swift-protobuf/AFTER.txt 11
repos/0095_3880_swift-protobuf/BEFORE.txt 167
repos/0096_3840_Then/AFTER.txt 0
repos/0096_3840_Then/BEFORE.txt 0
repos/0097_3827_KSCrash/AFTER.txt 3
repos/0097_3827_KSCrash/BEFORE.txt 3
repos/0098_3827_MarqueeLabel/AFTER.txt 3
repos/0098_3827_MarqueeLabel/BEFORE.txt 3
repos/0099_3818_AlamofireImage/AFTER.txt 48
repos/0099_3818_AlamofireImage/BEFORE.txt 48