Homekit-capable hard-wired switch - ideally two-way and intermediate.
It would open up so many possibilities to have a switch which could be hard-wired into circuits to give Homekit control, rather than just a plug-in one.
If it was a two-way (or even an intermediate switch for lighting circuits), it would allow individual circuits to have Homekit integration without needing a complete wiring centre or an RF switch in each location. We could switch individual zone valves / pump circuits / outside lights, etc.
The problem with an RF switch is that it doesn't allow two way (white wire) switching, so you can't control a 'motor on, motor off' valve, as, even if you used both channels on an RF switch, it's not easy to ensure only one is active at a time.
If the one product could function as an L1, L2, or IM switch depending on how you wired it, it would offer tremendous versatility for only one set of tooling.