My entire Gue'vessa Tau Axillery army was kitbashed between Tau and Cadians. I kitbashed the special weapons out of several crisis suit weapon systems. I spent upwards of 8 hours per special weapon manufacturing the new component out of the existing weapon bits, and by the time I figured it out I still had to make another 10-20 of them. If I could have made my prototype, took measurements with my calipers, then modeled and printed it, I would have had a much more consistent and pleasing army. At the very least I could have made fixtures to hold my remix of the GW kit together.
My intentions is to scratchbuild and fill in the gaps that GW has created. I feel its highway robbery that in order to model a Cadian with a plasma gun I either have to buy the command spru or buy a bunch of individual piece from a dubious online source or spend upwards of 10 bucks to buy them from Forge World. If they would bring back the bits store, I would probably not go in the direction 3D printing my own supplements.
I do see a future in which GW would sell DRM'd .STL or .IGES files that wouldn't be able to be modified. I also see them only supporting something like Stereolithography due to the quality that their own standards dictate.
Sorry for the ramble, I haven't had my coffee yet.