Going with the wave of pessimism here - Even if their contract still holds true after what was pretty much their final and farewell tour, the band has enough pull and clout with their label that they could probably pull out of said contract, even if it cost them money. If any album could be considered for release as long as it wasn't a straight-up re-issue, perhaps a rare live album could suffice, or an album of demos that they dug out of the vaults (B-Sides never exist, as they have said, but I wouldn't mind hearing the 10-minute version of "The Main Monkey Business", or other such pre-album demos). That stuff HAS to be saved somewhere, right?!
But honestly, at this point, considering it's been so long since the last tour and we haven't heard anything from the band about ANYTHING in the last year or so, I doubt we'll ever get a 20th full-length studio album out of them, and I'm ok with that. Clockwork Angels is a beautiful swansong for the band, and their last tour was a perfect capstone to a 40+ career, where the band called the shots and did it all for themselves.
I'd much rather not see them try and force out one more album and it not be what fans want, or worse, be something fans hate. Clockwork Angels is pretty much well-loved by most fans (that I have heard/read/seen), so it would be a shame if something else came out and it soured the end of their career.
-Marc.