Batteries have changed a lot and will continue to get better.
That's an understatement and a half. And, excluding how beneficial today's battery tech would be on its own, battery tech in the next 10 years is going to make exponential leaps.
All the things @will posted are true, PLUS
- batteries can run the same equipment on 2 or 3 rail interchangeably without issues
-no wiring glitches and birds nests of terminal blocks, block wires, etc. How big is that all by itself? And would allow much greater flexibility to change track plans organically without being tied to insulated blocks, switch locations, etc.
-you would easily be able to power a locomotive for 10 or so hour long sessions without recharge using the battery tech that will be available in 10 years. Recharging could be as simple as parking on a dedicated spur with a smart charging circuit.
-no more damaging shorts across rails. No more voltage spikes due to flaky source juice.
I suspect that the"electricity through the tracks" was just the best solution available to engineers in the 1930s when contemplating making their small trains run around. I bet if we showed Lionel techs today's batteries back in 1946 they would immediately abandon 18VAC through the tracks. At least, they would have if they were smart. Power distribution through a 2 or 3 rail bus for an application like trains is just so... Last century.
Edit: another data point: there is a currently active thread where a member can't get his GP7 to run in command mode and there's an utterly ridiculous (unironically serious) discussion about the merits of taping aluminum foil to the underside of elevated tracks to fix something called "ground plane interference". Really? We gotta tape tin foil to random parts of our layouts just to run an engine around in a circle? C'mon, if the benefits of getting rid of all sorts of current through tracks isn't obvious, I don't know what else to say.