Due to occasional limited wall space (or cosmetic considerations), many hardware stores sell two switches (both 2-way & 3-way models) in a single switch box form factor, often with Decora rocker switches. It would be nice if TP-Link offered a similar Kasa smart switch in that form factor.  Think of the HS-107 in a switch box.

I would instantly buy four to replace the standard ones I have.

It appears that no other smart switch manufacturer makes such a model, so Kasa would be the first.