I've mentioned before that I have a system for remotely running programs on my XT. Of course, since I'm running native code (mostly written in assembly code) on a machine without any kind of memory protection (and especially since I'm sometimes doing crazy things like disabling DRAM refresh), these programs will inevitably sometimes crash the entire machine. I don't want to have to go and reset it manually every time this happens, so I needed a remote reset switch.
I found this post on the Vintage Computer Forums describing a modification that is almost exactly what I want. Th exactly the modification I wanted to make, except that it's connected to a manual switch. It's trivial to go from a switch that grounds a line to programmatically grounding a line, though, so I just hooked it to the Arduino-based keyboard port manufacturing test device hack I already had, and now sending a particular byte over the serial line causes the Arduino to ground the power good line for 250ms and thereby reset the XT.