I had the same clever idea once. Deprecation warning, and it would (by the power of a C-Macro) auto-turn off when the relase x was reached, with louder and louder warnings before.

One day I came back from holidays. I had just broken a big go-live where the release number passed x. Date missed, next possibility in a few weeks. The team was pissed.

Yes they COULD have fixed the warnings. But breaking the go live was quite of of proportion for not doing so.