An updated and improved ATC has been in the mill for quite some time.
An improved ATC, and eventually the entire comms systems, is the next major improvement I'd personally like to see after dynamic campaigns.
Given and improved ATC has been in the development pipeline for quite some time, it would be nice to see it arrive sooner rather than later.
A slick, fairly realistic and fully functional ATC system would be such a game changer from an immersion POV IMHO.
I seem to recall in some of Matt's NTTR pre Alpha release demo videos (or perhaps it was one of the Q&A videos; I can't quite remember) they actually had disable the new ATC system because they were having a few issues with it.