I said SCAG-like book for one region. I think that's the bare minimum, with the 3E book serving as the master reference. I just don't want them to try to do Sarlona, Xendrik, etc. as part of "the entire Eberron setting".
One interesting quandary WotC is facing with Eberron is that, if they open it up on DMs Guild, there's an identifiable creator who would be able to publish material that many fans would view as more official than the WotC official material. On the other hand, the DMs Guild "contract" has an opening for WotC to use works published on that site, so it might actually fit into their plan perfectly, since they don't really want to produce too many source books, themselves. That assumes Keith still has an interest in working on Eberron and hasn't completely moved on to other projects, mentally.
Still, if Keith still has any interest in Eberron, I think the best case scenario is the regional (Breland, probably, but Aundair might be interesting) SCAG-type book that opens the setting up on DMs Guild. Then Keith can profit from filling in any holes that may need filling -- though I doubt the profit potential is quit-your-day-job level.