I was discussing something like this with my brother earlier and we came up with an idea, but I'm not sure how plausible it would be. This thread seemed like it would be the best place to post it.
Our idea was that they could make something similar to the Atari Flashback, in that it resembles the 2600 and plays games already stored on it. The system could come packed with a bunch so people could have something to play out of the box. The catch is that it could also have a slot for people to play games they already have, so if there's something not already on the system they could use their own cartridges. On top of this, Atari could set up a service like Wii's Virtual Console or the 360's Live Arcade for people to download other games that they want to the system, but for a fee. So basically it would be a normal 2600, but with a hard drive that people could download extra games to from a VC/XBLA-like service!
Maybe it's kind of stupid and unrealistic, but I thought it would be sort of cool.