Nethack is often brought up as a jewel of Open Source games, but its development style closely followed closed source methodologies. By comparison, most closed source early access games today have more open and transparent dev cycles than Nethack ever did. That's a side topic, but Open Source game design is a really interesting topic all by itself that I wish more people would talk about.
In any case, source dump models are in a lot of ways even better for downstream forking, because you don't have to regularly integrate new patches in. Whenever a new version of Nethack comes out you'd have to merge in the changes from that version, and then reapply whatever patches you made.
The wonderful thing about Open Source is that your patches don't always need to be included proper. :)
Don't bother. Just join the impatients:
http://nethack4.org/media/nethack4.git [email protected]:tsadok/nethack4.git
Some changes from NH4 trickle back into 3.6.
Not that it's your (or anyone's) responsibility to do this, but quick reminder that both Crawl and Nethack are completely Open Source. So if anyone ever wanted to do a downstream fork that was pure Crawl + a few Nethack features... they could.
Just want to maybe stick the idea in someone's head.