You're assuming the problem is "run everywhere all the time."
Plenty of projects are underway to get code that runs on "some of the machines very well all the time". asm.js, Google Native Client, and now that Blink has become a thing, I'll bet Dart gets it own VM in the most popular web browser in the world.
Plenty of projects are underway to get code that runs on "some of the machines very well all the time". asm.js, Google Native Client, and now that Blink has become a thing, I'll bet Dart gets it own VM in the most popular web browser in the world.