Nothing silly about it, people here have been on both ends of that conversation hehe, so I would say we all understand :).
It depends on the companies/people you plan to give the SDK to and their requirements and if you plan to give source code access.
If you cannot give source code out, my advice is to stick with Objective-C for a while longer as it will cause the least amount of support pain for you and will decouple your clients and you interns of iOS target and minimum deployment SDK’s and all.
If you go for binary Swift frameworks, the paths are two: one if you decide to wrap your framework in a thin Objective-C wrapper layer (this should allow you to use Swift 4.2/5 compiler and mandate licensee/users of the library use at least iOS 11 IIRC, need to double check @jrose is the best reference here, as minimum SDK and you will have both module and ABI stability helping you isolate your library from the Swift version and Xcode and iOS requirements your licensee may have) or an option that could work is to use the Swift 5.1 compiler (Xcode 11) for the library and iOS 13+ as target SDK. I would advise to start this once you and your users are all using Xcode 11+ and can target iOS 13+. From an app developer point of view I would prefer to wait for that scenario too.
Queue “small blurb” around it I wrote for one of our docs (forgive me everyone if there are issues with it... seemed to make good sense especially at that time):
If a third party developer shared a binary, pre-compiled, framework with us we need two key concepts to be implemented and working in order for our apps to build correctly: ABI stability and module stability. In short, we call ABI stability the fact that two binary pre-compiled libraries/apps have a stable binary specification to target and which you could use to have them communicate over. We say we have reached module stability when two separate modules can communicate with each other regardless of how they were built (different version of the Swift compiler, different versions of the Swift language specifications)
Summary: ABI stability means that two binary frameworks will work together at run time, but the compiler in Xcode 11 still isn't able to understand the framework content from Xcode 10.2. Starting in Xcode 11, however, there's a new format for binary framework module interfaces that's intended to be stable going forward --J.Rose - Apple
Binary Frameworks - Solutions and Future Proofing
There are a few solutions to this issue that would allow companies to best utilise the platform at hand while not being restricted by N third parties at once (this is from an app developer perspective not user perspective):
[All iOS versions] Write the libraries (binary framework/library) in Objective-C
[All iOS versions] Use Swift, but give the games’ source code to the app developers so that they are compiling all the libraries together
- It may require changes in the code in rare cases
[Xcode 11 / Swift 5.1] Use Swift, create binary frameworks/libraries
- [cons] App needs to compile for Swift 5.1 and libraries and app are built with the Swift 5.1 compiler from Xcode 11 or newer.