> it might completely upend the generational hypothesis

The generational hypothesis is about object lifetime, and that doesn't change.

It does change the relevance of the generational hypothesis to garbage collection.

> Surely someone's done some studies on this?

The go team has, and that's why go doesn't have a generational GC. The complexity of adding generational support, especially in a mutation-based language (so needing memory barriers and the like) was found not to benefit when a significant fraction of the newborn objects don't even reach the youngen. See https://github.com/golang/go/discussions/70257#discussioncom... from the current discussion of adding opt-in ad-hoc support for memory regions.