Why is LLVM Unsuitable for building a JIT?
I wrote HLVM, a high-level virtual machine with a rich static type system including value types, tail call elimination, generic printing, C FFI and POSIX threads with support for both static and JIT compilation. In particular, HLVM offers incredible performance for a high-level VM. I even implemented an ML-like interactive front-end with variant types and pattern matching using the JIT compiler, as seen in this computer algebra demonstration. All of my HLVM-related work combined totals just a few weeks work (and I am not a computer scientist, just a dabbler).
I think the results speak for themselves and demonstrate unequivocally that LLVM is perfectly suitable for JIT compilation.