Still, strong-typing has been with us forever and, in general, I feel like we've solved this problem. I'd like to see a light-weight VM framework that supports Java code compiled down to JS, with an in-browser Swing-like component framework (no, not applets). But a lot of the tenents of async, event-driven Swing style dev (including using workers to keep i/o off the event thread), actually overlay nicely with the challenges that modern JS frameworks are attempting to solve.
I know there's not a lot of Java-love around here, but, pick any language that has modeled out this problem and has a cadre of seasoned developers. Then, rather than re-invent the wheel, just port that to the browser.