A small rotary pump would be innovative, nothing like that exists currently. Vibe pumps are loud, but they are tested tech and live forever. A drop in replacement rotary pump would have a big market if it can stand up to use.

Are rotary pumps that large? From what I can tell, they’re relatively small as long as we’re talking the ones sized for single group machines.

Yes, they are pretty big. Just the pump alone is larger than the pump + motor for a vibe pump, and the motors for rotary pumps are like 4-5x the size of the pump. So you're really approaching 10x the size, it's kinda wild.