It is / would be a pretty simple SmartApp, but could be a little dependant on SmartThings’s scheduling which can be flaky. There are ways to write it to keep track of time of last powered time and retrigger, I hope. Does one already exist? I’m too lazy to search!
The other challenge?
Any of the energy reporting appliance modules (the Aeon you link is just as good as the SmartThings Centralite ZigBee version), will cease to report as soon as the power goes out. There is a slim chance it will squeeze out one less message to the Hub before the switch itself dies.
So the SmartApp has to force a poll / refresh … and I’m not sure what will happen when polling the “dead” Switch Device. Easy to experiment and find out.
This solves the problem because the original ST Motion Sensor can be installed with backup batteries, and thus can send the power outage event.
But it would be nice to avoid the need for another device.
So I’d still consider experimenting with just a power measuring outlet Switch.
I can run a test for you … I have that Aeon switch.