I think for safety reasons, it would be smart to just have your hot water heater turned up all the way (165F) than to have an external heater going hotter since people don't really know the proper way to safely handle the hot water hoses. Because if a hose blew on the homeowner, they would panic and get injured while the busted hose is flooding the floor they're on.
And once they're done cleaning, they can just turn down the hot water heater back to 125F.
As for the suction, I think it would be harder to install the correct vacuum motor in the central station in the house if it's more than just one floor to have the correct amount of suction.
And water pressure. That would be the easiest part. The same easy part would be the collection of solids filter box as well as the drain port for the dirty water.
So I think safety and suction would be the two hardest hurdles to get over