This is a great idea! I've been looking for something like this for some time. Watchdogs don't always work if you get a complete system freeze. Sometimes you have to do a manual reboot. That requires you being at the physical location or you need to do something like this. Sometimes you get a ultra hard lock in which you have to hard power the whole system (unplug everything, plug it back in), those are pretty rare though.
The problem with smart 'power' strips is they cost a lot, you have to consolidate your power, and sometimes you use more then one PSU per system so its' not a great idea.
Watch dogs don't help when the system is hard locked and can't even receive data.
This is a great in between and I've looked at something similiar that simply flips relays remotely. However, finding something like that which isn't just a hobby project is really hard to do. What other people are suggesting is great if you like to tinker, have 1-2 miners in a DIY sort of fashion, and you have a lot of time, it's not good for medium-large size miners or people who don't have a lot of time though.
However, I would agree with one of the other posters. Best implementation of this is a WIFI module with a relay. What he pointed out here: https://www.sparkfun.com/products/13678
If you can get those, one per system and just have them hang out above the breakout pins on the motherboard I would pay $15 a piece. Self powered from the LED cluster on the motherboard I think is do-able or one of the USB headers on the system. There are a lot of ways to do that.
One of the problems with the OP method is you have to run a bunch of wires from tons of systems to one central location and you have to have a 'monitoring' system on all the time. It'd definitely be better if it were integrated right into the package. It'd also be nice if you could still have a physical button at the machine available (this replaces the system power/led cluster instead of splitting it).