Yesterday, a slightly controversial commit got pushed:
Commit: #f2529f3 Rune lock. You need a rune to go to D:15. Downstairs of D:14 could be recoloured or replaced by a portal (maybe more consistent with D:27 zot portal).
This is a mandatory Vow of Courage I banner. The idea is quite old and was pushed after the 0.13 tournament so as to have as much time for testing as possible. You can read discussions about it on a old dev wiki page, or in several forum threads: here (locked), here (locked), here and here.
If the rune lock is considered to be good enough to stay for the next release, there will definitely be follow-up changes, cosmetic ones (locked staircase appearance, dungeon appearance before and after the lock) and balancing ones (unique generation springs to mind).