[Jach]

Re 3, people have known how to build real-time GCs since like the 70s and 80s. Lots of Lisp systems were built to handle real-time embedded systems with a lot less memory that our equivalent-environment ones have today. Even Java was originally built for embedded. While it's curious that mainstream GC implementations don't tend to include real-time versions (and for harder guarantees need to have all their primitives documented with how long they'll execute for as a function of their input, which I don't think Rust has), it might be worth it to schedule 3-6 months of your project's planning to make such a GC for your language of choice if you need it. If you need to be hard real time though, as opposed to soft, you're likely in for a lot of work regardless of what you do. And you're not likely going to be building a mass-market application like a browser on top of various mass-market OSes like Windows, Mac, etc.