We have tried the same thing years ago:
The main reason it failed because we could not decide who would lead the project, how to work together and what kind of game to make. All kind of ideas was flying around and finally I have just found my self on my own wit my own project.
I was developing it for some time and hope the community join at least with discussions of how to get things done technically, in theory with ideas…etc but eventually the whole idea of the open project is failed…
I would be interested to join an open-source GD project, but it would make no sense to start an other discussion about what kind of game to make. If you have anything in mind, just get started and take the lead, upload it to github and eventually people may contribute.