I'm hopeful for Rubinius w/r/t a long-term viable polyglot VM. It has _lots_ of languages built for it but Ruby is still its most popular and mature as far as I know.
I wasn't aware Rubinius was a polygot vm -- but are there any usable languages ported other than Ruby? Both the Smalltalk and Python port appear to be unfinished and abandoned?
Fancy[0] is one of the most mature languages on the VM other than Ruby I believe.