Starting fresh would take many more than two years, and very likely end in tears. This assumes browser vendors could spare the effort to do JS and the new thing (most cannot, even Google arguably can't).
For why the best VMs are focused on one language, see
https://www.dartlang.org/support/faq.html#q-why-didnt-google...
and
https://www.dartlang.org/articles/why-not-bytecode/
from the Dart team. See also
http://mozakai.blogspot.fr/2013/05/the-elusive-universal-web...
from Alon Zakai of Mozilla.