Yes, users either need to wait to adopt features or add conditionals to adopt them while still supporting other version. For instance, I needed to add some swift(>=5.5) blocks to Alamofire to support the new static member capabilities. However, this case, as Karl pointed out, is especially egregious, as, due to Swift's limited #if syntax, it requires duplicating the entire protocol definition to just to support some small bit of new syntax. That's basically the worst case scenario. Community adoption of the feature will be very low until they reasonably require the right version of Swift, which usually occurs once Apple stops accepting App Store submission with older versions of Xcode, and sometimes not even then. So any feature which can't be easily adopted with swift blocks will necessarily lag in adoption, which is bad for the language.
Of course, there are a lot of things Apple could do to help this case that aren't related to the language it self, but...