Having spent a few days reading, an idea that occurred to me was a 68k-> asm.js compiler and then take advantage of the various JavaScript JITs to speed emulation.
I'm not sure that will be as fast as using LVVM to generate native code, although for running in a browser I think you can use LVVM to generate asm.js (or at least there are people working on something like that).
http://en.wikipedia.org/wiki/EmscriptenI don't know how dynamic it can be though, i.e. whether it can cope with self modifying code or even programs loaded into ram.
To work you'll need to be JIT the 68k to asm.js and detecting when to push new asm.js through to the JavaScript JIT. If changing one byte in memory means flushing the entire JavaScript JIT cache then you'd be quicker running an interpreter. I don't even know if LVVM is really up to being used for a general purpose emulator (it might however work well in a contrived case where specific assumptions can be made).
