BSD Unix is a possible model. I was at UC Berkley in a computer science research group when BSD evolved.
Ken Thompson and Dennis Ritchie developed Unix at AT&T's Bell Laboratories in the early 1970s. In January 1974 Professor Bob Fabry obtained a Version 4 tape and it was installed on a PDP-11/45 at UC Berkeley.
AT&T corporation saw that Unix was successful and dealing with them became more difficult.
A number of extensions, fixes, and improvements were developed by users of Unix. Bill Joy collected these and released a tape called first Berkeley Software Distribution (1BSD). This was an add-on to Sixth Edition Unix from AT&T.
This process of support evolved until DARPA provided funding to make 4BSD a free open source OS for computer science research.
Development of BSD Unix was guided by an amazing committee:
To guide the design of 4.2BSD DARPA formed a"steering committee" consisting of Bob Fabry, Bill Joy and Sam Leffler from UCB, Alan Nemeth and Rob Gurwitz from BBN, Dennis Ritchie from Bell Labs, Keith Lantz from Stanford, Rick Rashid from Carnegie-Mellon, Bert Halstead from MIT, Dan Lynch from ISI, and Gerald J. Popek of UCLA. The committee met from April 1981 to June 1983.
User support from the Arduino group is non-existent. A first step could be to collect fixes and improvements in a well known place.
This would be along the lines of what Paul Stoffregen is doing, not forking the project.
Some open structure needs to be setup to screen and organize submissions so users can easily find and install what they need.
Another step could be a discussion space as pico mentioned where the main topic is how to organize an open user support group.
FreeBSD evolved from the UC work. This is a key statement about the organization of FreeBSD:
The FreeBSD Core Team constitutes the project's "Board of Directors", responsible for deciding the project's overall goals and direction as well as managing specific areas of the FreeBSD project landscape. The Core Team is elected by the active developers in the project.
So to have a say, vote, you must contribute.