Hi Neil,
You sound like someone who might be able to help and maybe I can offer a few suggestions for switch design. I've been experimenting with various models of remote operated switches, including Home Easy, Varilight, Broadlink and not to mention various Chinese devices from Amazon.The main gripes I have with pretty much all of the designs are:
1. Incompatibility with existing switches on 2 way and intermediate switched circuits.
2. Often require a neutral wire at the switch
3. Led lamp incompatibility
4. Non reporting of status
5. Remember previous state
I've been looking at designing a switch which uses a mechanical latching relay rather than either solid state switching or single acting magnetic relays. By utilising a double pole double throw latching relay, the contacts can be used for single way, two way or intermediate switching and you would only need to replace one switch in a circuit, no matter how many intermediates were fitted as the latching relay behaves exactly like the physical switch contacts of a conventional light switch.
The wifi receivers I would presume use such little power they could draw from the series connection with the light or lamp and for the relatively higher momentary current draw during relay toggling, a capacitor should store enough energy to avoid the light from flickering on excessively.
I have some plug-in wifi switches which I bought at Aldi (Silvercrest) several years back and these switches report status via the phone App. I was looking to see if I could utilise the circuitry from these to drive the relay but haven't measured the quiescent current draw yet so unsure if they will run on just a switched live without neutral.
If you are in the game of the software end to control, I'd be interested for some contact and possible collaboration.