Current processors already do that. You don't see the true number of registers or the true instruction set/format of any modern Intel processor. x86 instructions are translated into micro-ops, so x86 is really just a compatibility layer.

I do agree that current processors optimize for C/C++ (although of course there are niche systems like Azul which optimize for other languages). It would be nice to have processor extensions that allow us get better GC performance, or better handling of immutable values. There's a chicken-and-egg problem getting there.