The red zone is one of a number of features that can cause much hair-pulling when enabled on platforms that don’t support it. Any amateur OS implementers using Rust who don’t stumble on this particular blog post (which explains how and why to disable it) are in for a world of pain.
I’m thinking that the red zone should be off by default, and enabled in target files (such as Linux) that support it. The only downside of the red zone being off is decreased performance, which I think is a much better default than occasional stack corruption.
Addendum: another feature which would should be off by default is landing pads, for the same reasons.