If all you need is a static IP and a little traffic, there are free-tier or a couple bucks a month vps options. Use SSH to proxy a single port to connect to their service.

Your idea works in theory, but in practice, using a ZigBee plug as a power sensor -even if you managed to program a way of detecting its online/offline status, will probably have too many issues.

The protocol is designed for low power and so has to be robust to temporary connectivity issues from interference. You would either have too much latency between the switch and the light turning on/off, or you would have phantom switching of the light whenever some other device in your house desides to do its thing.

It is a genuinely neat idea you had though.

Agreed. I smiles at the blunt: no need to talk about this, just go try this. Then I read the comments. Guess I should call my dad.