As a former R/C oval car guy, I see a continuation of battery size coming down and battery power and run time going up. The key to running model rains with battery power will be to eliminate the hassles of charging or disfiguration of engines or rolling stock with on-board charging ports.
The solution is a system that will allow charging through the track while the train is operational and/or charging through the rails on a separate siding to which the train can be moved. Both of these systems would result in no charging port necessary nor having to remove the battery from the engine/rolling stock in order to charge the battery. I believe there are companies working on these now.