Is this really the great bottleneck, though? Interior modders have always been in relative abundance compared to modelers, quest and NPC design, etc. If we factor in templates and cookie cutter designs, this part of the workload is already much reduced. We do not need interior modders sitting on their hands waiting for the rest to catch up, we have enough of that already.
I strongly oppose any notion of filler buildings without interiors: this reduces our environments to pure decor, and goes against the grain of the kind of freeform exploration that is the hallmark of TES games.
Looking at the Anvil overview, there are a couple of places where we can cut or simplify interior work: some of the worker houses/locations that are there from a practical point of view can be cut in the name of conservation of detail, some of the warehouses and poor houses could be joined together in larger, connected buildings (warehouses especially are a bit too numerous), and a couple of things like shrines and shops could be exteriorized as open-air shrines (Kynareth) and market stalls. However, and I can't stress this enough, we cannot make any decisions about this until Praedator shows up. We're not going to start messing with people's claims behind their back.
Other than that, I think the projected scale of future settlements actually looks pretty good. roerichs concept for Sutch here
strikes me as a decent indicator of scale, comparable to cities like Gnisis or Suran. Kvatch, our next big city, was always going to be smaller than Anvil due to its geographical restrictions.