The Greater Bristol Strategic Transport Study contains a map (figure 5.4, Bath Rapid Transit Network) that envisages a busway over the old MR line in Bath, running from Homebase, on past Weston station, all the way to the river crossing at Newbridge, where it would join the A36. There's a kink in the route to avoid the embankment behind Kingsmead Motors, and possibly to link into the aforementioned Western Riverside development.
As far as I know (which isn't very far), the AVR's long-term plans are only to lay track as far as Newbridge, so the two could dovetail quite nicely. However, I won't be holding my breath for either scheme to come to fruition.
Gary