Yes, that's one answer. But I actually think you can absolutely have both in the same compiler. But you need to have two backends, as I described. You use the custom backend for development (fast to compile) and you use LLVM for release (fast to run).
Well yes, but at that point aren't you effectively writing two compilers in one? It seems to me that would be at odds with wanting it to be fast to compile itself (you said under 30s) and would make it more difficult for the uninitiated to contribute to.
I don't mean to discourage and I don't disagree with the aims. I just have the (possibly mistaken) impression that compilers inevitably fall on a continuum from simple and fast to complex and slow.