You could definitely zero registers that way, and a allocator that zeros on drop should be easy. The only tricky thing would be zeroing the stack - how do you know how deep to go? I wonder what Go's solution to that is...
And stack's the main problem, yeah. It's kind of the main reason why zeroing registers is not enough. That and inter-procedural optimizations.
In general though getting to a fairly predictable place is possible and the typical case of key material shouldn’t have highly arbitrary stacks, if you do you’re losing (see io comment above).
https://docs.rs/zeroize/1.8.1/zeroize/ has been effective for some users, it’s helped black box tests searching for key material no longer find it. There are also some docs there on how to avoid common pitfalls and links to ongoing language level discussions on the remaining and more complex register level issues.