Defrag currently exists as a stubbed gamemode, meaning the basic gamemode type is in place (currently just surf settings with a rocket launcher) but the full implementation i.e. VQ3/CPMA movement, Quake weapons and defrag-specific maps won't be worked on until after 1.0.0. The focus currently is on getting the public beta out, which will include the finished modes (Surf, Bhop, Rocket Jump, Sticky Jump and Ahop) as well as Conc and Tricksurf as they're relatively close to finished and the communities would most benefit from Momentum support. Focusing on other gamemodes like Defrag risks slowing 1.0.0 release, so we intend to hold back on them.
Post-1.0.0, Climb, Parkour and Defrag will get worked on more actively. Of these, Defrag is quite likely to take the longest, as it requires bringing over Quake movement mechanics, will need more discussion of exactly what weapons to include, and is going take a ton of testing. There's also the question of map size, as Defrag maps are often too large to fit within the Hammer grid.
So whilst Defrag is something we want to do - Quake movement is awesome and something a lot of Source players should have fun adapting to (🙃) - it's on the backburner for now. After 1.0.0 is out it'll certainly get some more love!
Lastly worth noting that whilst work on the base game is now closed source, it'd probably still be possible for people to fork 0.8.7 and work on modes like Defrag, which could potentially be merged into the game post 1.0.0 (just give Gocnak a shout before starting on something like that).
(This is probably an overly long response to a single word post, but hey, good to get this stuff up on the forums)
