[sehrope]

Any background on who's doing this or what the motivation is?

The linked site doesn't have much content besides a link to the GitHub repo.

EDIT: Even though it's not explicitly listed in the README or contributor list, the commit history does show a bit of detail: https://github.com/iojs/io.js/commits/v0.12

[mawburn]

Wired has a pretty good high level overview:

http://www.wired.com/2014/12/io-js/