If your water heater is on a outside wall your best bet is to run a pan drain through that wall to the outside of the house. Nothing else needs a pan or a floor drain. Most bath and washrooms in my parts rarely have floor drains in them. Maybe have your W/M drain routinely snaked out for peace of mind. That is gonna be your only other real threat other than just freak accidents. But your floor drain idea isn't out of the question. Just some jackhammering involved. But tying a pan drain into the vent stack just isn't very practical. You would have to raise up the appliances and cut in a sanitary tee and install a p-trap for the drain to dump into.