At least someone at Sun gets it: Gilad Bracha is helping push the idea of hot-swapping in the JVM (JSR 292). However, it's no simle problem for them:

Now before you get all excited, I need to be very clear: we are not making any promises with respect to hotswapping. Full hotswapping support in a system with mandatory static typing remains an active research topic. We really don’t know how far we can go.

There's the problem, of course - locked in the static typing dungeon, they now see that the grass really is greener on the outside. The trouble is, getting there won't be easy, and may not even be possible - given where they are now. This all could have been solved back in 1995, had Gosling been an actual visionary. Too bad he still hasn't gotten the memo. In the meantime, Gilad knows what the benefits are:

This reluctance to commit doesn’t stem from a lack of support for hotswapping, or a lack of appreciation of its value. As an old Smalltalker, I know what we’re missing here. Once you’ve used a system with these dynamic capabilities, you’re hooked for life.

Which is why I'm a Smalltalker :)