Imagine all of the 1-2 decade old applets that no one will care enough about to update. I'm thinking of little physics simulators you'd find on a professor's web page to simulate projectile motion and such.
Maybe we just need a shumway [1] equivalent for Java Applets.
Mozilla had been working on a "j2me.js" VM called PluotSorbet. The primary use case was to host J2ME apps on Firefox OS.