Question is, are they removing support from the OS frameworks themselves or just Mac App Store? There are many applications that still use GC, many of which are not in the store. Does that mean they cut support for these in a future 10.10 update or 10.11? I doubt it.
I'd bet on 10.11 or 10.12. ig they don't eventually remove it, there's little point in deprecating it or forcing it off the App Store as they can not reap the benefits in their own code.
At the very bottom of the documentation page linked from this page [1], it says it will be removed. Sounds pretty definitive to me.
Garbage collection is deprecated in OS X Mountain Lion v10.8, and will be removed in a future version of OS X. Automatic Reference Counting is the recommended replacement technology.
