So instead of thinking about creating another mod, it would be better to offer Kell a hand, as he is currently stuggling with finishing a new version of Quoth since necros doesn't have the time. This way, some of the features mentioned above could be incorparated as well.
I agree about the 'extra progs.dat for tiny changes' thing (e.g. in bbelief), but then again it has to be taken into consideration that many of the possible hacks (feasible with standard progs) were only fairly recently discovered and preached upon us

And, yeah, such an encompassing mod could never include every possible feature needed for certain maps - and if a mapper wants to include new monsters or a new boss than it is legitimate to have custom progs no matter what.
I like Preach's idea of a code repository, though, of course, with regard to the spirit of this discussion it is bound to put people off.