Thanks for kicking off the thread @mbalex99! It was great to catch up during FOSDEM 
The topic indeed has been lingering around for a long time, and it may be time to give it a shot for real.
I was talking with @Douglas_Gregor last week to see what's missing so we could formalize cdecl, and it does not seem to be that much missing.
The main things seem to be:
- ban objc types from
@cdeclannotated methods- but allow them with
@cdecl+@objc
- but allow them with
- introduce @cdecl support for int backed enums
- some cleanup in generated headers -- like the
__OBJC__attribute and how blocks are handled (if objc)
There's some other problems Doug had more context on, but it does seem like something viable to consider in the near future...