One of the key things in Sean's "Safe C++" is that, like Rust, it actually technically works. If we write software in the safe C++ dialect we get safe programs just as if we write ordinary safe (rather than ever invoking "unsafe") Rust we get safe programs. WG21 didn't take Safe C++ and it will most likely now be a minor footnote in history, but it did really work.

"I think this could be possible" isn't an enabling technology. If you write hard SF it's maybe useful to distinguish things which could happen from those which can't, but for practical purposes it only matters if you actually did it. Sean's proposed "Safe C++" did it, Zig, today, did not.

There are other obstacles - like adoption, as we saw for "Safe C++" - but they're predicated on having the technology at all, you cannot adopt technologies which don't exist, that's just make believe. Which I think is already the path WG21 has set out on.