Firstly, let me start by providing my motivations:
1) I'm not a fan of proprietary closed-source software. I understand it's unavoidable in the current state of the world (trade > deed), so I'll keep my Utopian views out of it for the most part.
2) Since we're given the tools to develop these add-ons (insim...etc) freely, it seems only fair that the development work done on them be freely shared as well.
3) 1 & 2 being said, I don't want to put the image out there that I want to "change" other projects or pressure any existing project to open up.
Now, onto the heart of my idea:
I think the "open-oriented" developers on here (and there are a few that I can see around) should get together on a few projects, one at a time... I've worked with number of community based projects before, and the enjoyment of working with a diverse set of people is great.
If I had to throw a few ideas out there now I would say:
1) Glade-like UI class to be used in any project. (
http://glade.gnome.org/) basically, building UIs based on XML ... then interacting with the glade object to manipulate everything...a little cleaner and simpler than the current "every UI element is an Island to Itself" setup.
2) "Points" server setup. Much like the popular "points servers" now, but have a central DB for it, and allow people to create leagues ... etc, of their own, all running this as their core admin. Would be the larger in scale than most projects...requiring a web front-end as well.
3) Cruise server. I know most of us (myself included) don't particularly like cruise servers, but as a "development challenge" it would serve the purpose well. On top of that, it would provide a more "satisfactory" answer to the parade of cruise server requests and questions....
I have other ideas floating around...but I think these are the 3 that seem to stand out in my head as a) having the most impact and b) being fairly challenging and, in the end, rewarding.
Takers? I plan on starting on one of the 3 projects (likely the Glade-type engine) soon...
Lastly...for the "important" stuff. All code/assets of the projects will be GPL'd. All source for all aspects will be available. Obviously some components will be in compiled libraries (dlls) but code will be provided for those as well.