Open source hardware - is it just for a reference?

Today I was talking with Brandon about an open-source hardware community project.

Open-source hardware is quite different from open-source software. In software you can work on different aspects of the project and can make contributions. On the other hand, for hardware this is very challenging.

One cannot have a person working on one corner of the board and another working on some other aspect of the board.

The only successful open-source hardware community that really succeeded is the RepRap project to my knowledge. While there are a lot of open source hardware projects, they serve more or less as a reference. You could make changes to them in your own fork but pushing back the changes is rather rare. And accepting those PR especially on the PCB is even rarer.

I think there can be multiple people working on the schematic, but having many people working on the same board is very challenging. If you have any things to add to an open source hardware project, how would you do it? Make changes in your own fork? Or tell the devs about your idea

Looking for insights on how to make a community open-source hardware project.