The idea is great in the same way the idea of a perpetual motion machine is great: I'd love to have a perpetual motion machine (or C++ modules), but it's just not realistic.

IMO, the modules standard should have aimed to only support headers with no inline code (including no templates). That would be a severe limitation, but at least maybe it might have solved the problem posed by protobuf soup (AFAIK the original motivation for modules) and had a chance of being a real thing.