If you had a code base in Rust would you consider rewriting it in a language with First-class GPGPU support, a mature ecosystem (including some of the highest quality, most efficient code that exists), vastly superior tooling and multiple established compilers?
Depends on the codebase. If one of those things could qualitatively improve my codebase - for instance, by introducing GPGPU support and speeding everything up by an order of magnitude - I very well might. Ultimately, it's a cost-benefit calculation that has to be done for every individual case, it's not something you can answer in the abstract. None of the language features of Rust can offer a similar level of advantage, except perhaps in cases where (limited) static guarantees of certain kinds of memory safety are of critical importance.
If my code runs slow because of lacks in one of the things you list I'll probably rewrite that part of my code. Note that I wouldn't rewrite everything, at least not at first.
In almost all cases though, the that fact that my codebase is working means the ecosystem, tooling and compilers are good enough as is and so I won't have a compelling reason to rewrite. I can get great programmers productive in Rust faster than the boss can figure out that neither I nor the new guy knew anything about rust on the first day.
Typically the only time the factors you mention come into consideration is a brand new project. I will generally know before I write the first line of code if I need GPGPU support or not. I ecosystem, tools, and existence of compilers are just a few of trade offs I will consider.
