That would most likely take longer or as long at best then the current system they have in place for going from resort to resort which is go to the nearest park and transfer. Back in the day when resorts sharing busses was common, travel times were much longer. Taking a bus to DHS from the Contemporary involved stops at the Poly and GF before you even began heading to DHS. It felt like you were going to DHS by taking a "short cut" through Tampa.That may be true but they don't really have to have ONE bus for each resort. They could have ONE bus that goes to like 3 different resorts that are near one another. I really think, from the beginning, back in the 70's they should have considered extending the Monorail gradually so it hit all the resorts and parks.
Yes, very costly, but doing it gradually could have not only been feasible but it could have eliminated all the busses. Big cities have subway trains taking you everywhere. I think Disney is like a big city.
As has been pointed out, the problem is volume. There simply is not enough for dedicated routes and once you start sharing or combining routes to increase the volume, you eclipse any time savings over the current system.