Other than that very few people get paid to develop perl when compared to the JVM and Java JIT systems, I'm not sure what else would be preventing this. The P5P work very hard to improve the major targets for perl as it is, and I'm not sure that adding another target is on their radar. The Perl6 and Parrot hackers are busy doing their stuff, too. It'd likely need to be a dedicated port team tasked with building and maintaining such a beast.

I'm not sure if Tk or Gtk2 would even be the best display technology, at least at first. That would target Flash and Silverlight pretty handily, though. What might be better at first is to interface to the JavaScript HTML and CSS DOM. Using Perl's strengths to manipulate the pages themselves could be really nice.