"Are you referring to compiling Scala to Java bytecode, running that on VMKit over LLVM,"
No, I'm talking about compiling Scala directly into machine code using LLVM. This is doable and is not particularly hard, it requires only a new backend for Scala.
"and using an Unladen Swallow inspired GC? Or are you talking about something even cooler?"
I'm talking about Swallow's GC.
"I know that Mono can use LLVM as the backend. I guess it takes a bit longer to JIT but the resulting code is faster after that. Perhaps your Scala scenario would benefit Mono as well."
Mono's LLVM experiment is not complete, it can't be used in production.