I’m not opposed to doing the same for modules in their own files. However, I personally don’t need it, so didn’t think to include that. That’s what feedback like yours is for 
I’m not sure about compile times because I don’t know how rustc handles modules internally.
However, I do see a potential for more memory consumption, as needing to find multiple mod blocks/files in order to “compose” a module means the first N-1 mod parts (assuming N parts total) need to be stored somewhere until the last part is found.
That said, the option is clearly viable in principle, as something very similar is already happening for impl blocks today, at least conceptually.
I wasn’t aware this was more than a passing thought a couple of Rustaceans had in the vein of “wouldn’t it be nice if …”. To determine the effects, if any, I guess I’d need to read the relevant RFC for parameterized modules. Is there a link to it somewhere?
Perhaps impl blocks can offer some inspiration here as well: they can be parameterized (if the type to which the impl block is associated is also parameterized), and they can also be split up into multiple blocks. I’m just not sure if both are possible at the same time.
If so, why not do something similar with modules?
And if not, why not copy that behavior to mod blocks?
