I suspect there'll be cross-platform issues they want to solve later than sooner and thus why keeping it single platform.
Atom is a proof of concept at the moment. I don't even expect a "html5 based editor" getting prevalent.
Yeah, I'd say that it's picking up some steam.
Mostly enthusiasts on HN, r/programming and the like.
The vast masses of programming don't care for LightTable (or Clojure, it's core language).
Atom.io is too slow for most Sublime users, especially on hardware that is not bleeding-edge.
I've been using it on and off since the initial release. I'm not particularly impressed by it so far; in particular, the performance relative to ST3 is absolutely appalling in every respect. It's still in development, I understand - but one of the key awesome things about ST3 is how amazing, earth-shatteringly fast it is.
What I'd like more than Atom would be an evolved version of Sublime. There's still a little bit of cruft in there from what I can see - while I've never developed a plugin, I've heard it's a bit tricky. I'd love something with proper support for things like SublimeREPL more extensive capabilities for previewing documents, and perhaps better ways to theme and write plugins using alternative languages.
I'm not totally convinced that Github are going to be able to make Atom a compelling offering on the whole.
This makes it really hard for new proprietary editors like Atom or Sublime Text to just come along and be better than these existing monsters. Personally, none of them has what it takes for me but I see reasons to believe they can stand a chance in the near future.