You might want to look at Tim Bray's blog on the subject:
Sun is a big company. Tim was the guy who made it happen, and he has some really cogent comments on why it was JRuby, and what would be needed for Sun to hire another language guru.
As the Python FIT maintainer, I've had a request to make it run under Jython. I'm not going to do it for two reasons, one of which is that I'm not a Java guy. The whole ecosystem is a foreign language for me.
The other is that my current support base (minimum Python level) is 2.3. AFAIK, Jython is still stuck on 2.1. If someone wants to step up to the plate and make it run with Jython (or IronPython or PyPy for that matter) I'll certainly discuss applying the patches. However, I'm not going to go back on the minimum level of Python required.
The takehome is that if you want Sun to support a couple of Jython developers, talk to Tim. But I suspect that the people in question will have to show their interest in very concrete ways first.