I think Sublime could still compete if some basic things change for Sublime. Sublime still has time.
Atom appears it won't be free when it is complete, so you will have to pay for it just like Sublime.
Atom still lacks quite a bit of functionality that needs to be built up as official packages. Sublime is always going to have an advantage with speed due to using native code (I am interested to test how much of advantage, haven't had a chance to really test extensively). Atom really needs a better built-in package manager (browsing and installing needs to be better). Needs to be able to manage projects...seriously, how is that not already in there.
With that said, Atom is extremely modular. Everything is a module which allows for ridiculous customization which lends itself to even cooler plugins since you can design web interfaces into a tab for a plugin, probably create your own overlays etc. Probably allows for people to mess things up with their plugins more too, but I guess there is always a price to pay for high customization. For web developers, I feel an editor that is a web browser is going to have some serious advantages over sublime.
But the big advantage of Atom is going to be support. If Atom in the end is so close to Sublime functionality, enough that people can easily switch, and the price is comparable, and the speed close enough, the added benefit of support in Atom will probably be the nail in Sublime's coffin.
If sublime would spend serious effort on the current bugs, and iron out some things to be more consistent in the API and such, I think Sublime could still be a contender in the future. I think if Sublime added better access to render interfaces for plugins, that would make it a very good contender. I don't think it necessarily has to expose everything like Atom does. I used to love customizing the heck out of Linux OSs, but these days, I find it exhausting. I don't need to customize everything, just the things that matter. I'm also not a web developer, so I don't really need the web advantages that Atom potentially can offer. And because I'm not a web developer I don't really know how big of an advantage Atom actually has as an editor.
Atom is not ready for enough for me to jump ship; maybe down the road. I would be interested to hear Jon's take on Atom...