As I understand it, the reason the drum sample libraries are so huge is that there's a lot of redundant information - BFD2 and their ilk tend not to use Modelling per se (which is how your Roland TD-Whatever keeps its memory footprint down)....Going back to the example of the Mic Positions - on BFD2 you've got 4 main sets of mics for any given drum, and then things like bleed). hence the huge libraries.
Once you get your "meta" kit setup just right though, exporting the sounds with perhaps 5 or 6 variants of each drum to avoid machinegunning, I should have thought with 3:1 (ish) lossless compression algorithm that's been mentioned, I don't think kits would necessarily be all that big, because they don't have to have the "dynamic" characteristics of these drum samplers.
I just think if there's going to be a Editor with this sort of gui coming from 2box, why not build it within a VST framework from the ground up?