It's not quite as simple as that :) I think upstreaming half of gofumpt's additions to gofmt would be reasonable, but the person who wrote and maintains gofmt is Robert Griesemer, who continues to be quite busy with generics. They are still actively fixing typechecking bugs and performance issues, as far as I can see.

I think it's hard for anyone to justify pausing or distracting the generics work in favor of upstreaming parts of gofumpt. At the end of the day, gofumpt works today - it's just a bit awkward to have it as a third party tool.

That said, it is on my radar to talk to him and make a plan for upstreaming.

Edit: to clarify what I mean with the above: I of course could do the legwork to port my formatting changes to go/printer, the guts of gofmt. The reason I mention Robert is that he'd be the one to consider and approve each formatting change, and review the code changes and tests. That work is trickier than it sounds, because you have to think about the possible effect any formatting change would have on all kinds of existing Go code out there.

For open source projects in general, and the Go project in particular, I think it is easy to underestimate how much maintainer time is consumed discussing & considering whether a change should be made.