Make is your friend.
I collaborate on dropbox with make-unfriendly computer-unsavvy people, make is not an option - and this is not such an uncommon case I guess! Instead, an _editable_ file format that __guarantees__ you have all is needed to compile the file is a haven for data integrity.
All the rest, I am sorry, is too geeky-pretensions-minded in my opinion. This kind of thinking in my opinion is ultimately the reason of the same attitude that causes some people never get over the learning curve of LaTeX. Do you want to collaborate with just computer skilled people? or you want to collaborate on writing just as effectively with just anybody? if you opt for the second, then LyX is a great solution, but the need to carry around figures is still a burden for some. Is this clear? (I said for some, maybe is not a problem for me, not a problem for you, but is a problem for the other half of the world! try to wear their shoes every now and then!)
So, if you wanted to use make, then for most users you can as well suggest to use LaTeX on vi :) is as much difficulty (infinity!)! Going by this token one always ends up saying "my current implementation can do it, just do 1), 2). 3) n) steps, but what effort does it take? Before answering think about your grandma having to do it ...
