I develop an app along with a framework that it bundles. Because it's bundling the framework, there's no need for ABI stability in the framework, as there's no way to load a version of the framework other than the one it's compiled against.
Unfortunately, the new opaque result type feature of Swift 5.1 seems to force the use of resilient types and requires runtime support, meaning it can't be deployed earlier than iOS 13 / macOS 10.15.
Weirdly enough, in a quick test this is actually true within the same module. I assume that's a bug (SR-10925) as there's no reason at all to require resilient types within a module.
In any case, even assuming that worked, I'm very interested in being able to add APIs to my private framework that use opaque result types, but the only way to do that is to have some mechanism of saying "disable ABI stability behavior for this module". I'm not aware of any way to do this now. Has this been discussed before?