I'd say it's because everyone has his own taste and we're all doing it for fun (and for no money). So your "network" idea is fine but unless these people you mention don't share the same goals and expectations from this new machine, you can't force them.
For example -- I totally don't care about MIDI ports, I want DSP and general Falcon compatibility as the priority. Someone else is more into PowerPC or even Intel CPU and don't care about Falcon compatibility at all.
Maybe I'm wrong but I think you're not a programmer -- it's easy to shout "people, let's cooperate on project XY" but the programming is mostly boring and long work with uncertain results. You simple can't force anyone to do that for free.
Moral conclusion is you have to find people with the same ideas, good knowledge and experiences and persuade them to make something like new machine :)