Floor heat sure sounds like a good idea........
However comma,
There are a couple of things you need to look at.
1. Defrosting the windows? How is a floor heater going to do this?
2. Heat for the front of the bus, ie driver compartment.
I would not remove both heaters, front one will be needed for winter driving, rear one sure would come in handy if needed....
Radiant heated floors sure would be great on those cold mornings.......