I'm not a PL expert but isn't building a decent JIT a massive undertaking? I guess you're saying that the JIT itself would be what makes a project like this worth using in the first place?
It's like most things in software, if you constrain the problem enough, focus on the problems you actually have and make some smart choices early on, it can be a very modest lift on the order of a week or two for a 90% solution, but on the other end of the spectrum, it's a lifetime of work for a team of hundreds...