Yes, it is possible to load multiple wasm modules but there are some caveats that make it an advanced topic. I have done this before, though. One issue is that record type descriptors are not canonicalized between wasm modules, so if you had record type <foo> in modules A and B they would be completely different types.
Whole program compilation is just kind of a slow thing in general. We are trying to make compilation less frequent during development by improving the tools for live hacking. We're not there yet, of course, but it's getting better.
I don't understand what you mean by "it can't reload functions"?