This is fair, although this places some mental load on the programmer because they need to be careful when dealing with generics / operator overloading or when extracting helper functions.
> noexcept functions if we are talking about C++
This is a good C++-specific guarantee. But it's probably outweighted by the C++-specific lack of guarantees. "Operations on basic types" can now invoke UB, if we are talking about C++.
> Isn't it too much clutter?
In cases with one generic parameter, like the ones I demonstrated, I think it looks ok. Normal generic code. Rust generics are only going to require less ceremony in the future, because the team keeps making progress on implied bounds, lifetime elision, 2024 lifetime capture rules.
> What if a function has three arguments? You'd need three generic parameters for their errors.
This really depends on the context and what the code actually does, and needs a concrete example to discuss. I don't remember seeing a real world example with three Result parameters, nevermind having generic but distinct errors in them.