Given that Perl works on both Linux and Symbian (a Java-based OS), then I think we're pretty safe. As for it running X, that's really doubtful. X is HEAVY and has a bunch of functionality that isn't needed (though doing an X-term to your friend's phone would be kinda cool ...)
My criteria for good software:
Does it work?
Can someone else come in, make a change, and be reasonably certain no bugs were introduced?
(nit: Symbian isn't Java based, it's implemented in C++. Java apps can and do run on top of Symbian via J2ME, but they're not considered native, only C++ apps are).
Google have written their own UI toolkit for their new mobile OS (not unlike Qtopia). I don't know if that will use X, but anyway that will be seamless to the application developer.
I would guess that it's a question of whether the Perl interpreter can be ported to the new OS, but as you say given that it was ported to Symbian years ago (on devices far less powerful than the ones coming out now) and of course Perl works on Linux, my guess is that it would be possible.