I’d expect this would need to be like a heartbeat / dead mans switch, I.e keep flagging as up, and when you stop flagging, it’s considered down. Otherwise you would need a different status monitor to monitor the status agent…
Which is fine. Having a standardized .status domain for the pages, even if manually updated, is a big upgrade from the hodgepodge of what's out there now.
It'd be easier, and cheaper eventually, to have it on a properly sharded database, maybe with a few different DNS and server front ends.