This is a deal breaker for an IDE, IMHO. Then again, it is a really young editor and has a lot of room to grow and mature. So, here's to both Lime Text & Atom. May our text processing future be bright!
http://blog.atom.io/2014/07/02/moving-atom-to-react.html
Beyond that, there are also more performance optimizations coming:
https://github.com/atom/atom/pull/3154
The only two things I miss from Sublime are "find in project" and "go to symbol in project". Atom's implementations of those need some work. But everything else is as good or better than Sublime. And it's really easy to contribute and get pull requests merged.
As far as I can tell from watching development, GitHub has at least 4 full-time engineers working on Atom.
You can do pretty much any UI you can imagine using a website in some way and Atom allows you to do exactly that. You can modify the entire UI and this is what I was always missing in ST: The ability to modify the UI more extensivly.
Sadly, this all leads to the very downside that everyone knows: Performance. Computers will eventually get to the point where Atom feels as fast as Sublime, because 1) the coding was improved and more significantly, and 2) CPUs will get good enough for Atom that a human can't see differences between Atom and ST's performance, despite ST being way faster still. It's always been like that.