So I was looking over my world, and realized that gold wasn't exactly bountiful for me. And me, wanting to make a minecart system, was going to have trouble without boosters and without powered rails. Then it occurred to me that electric minecarts make a lot of sense! They're work about the same as your usual powered minecart, but run off batteries (hopefully with a GUI window to load and unload) and might have a better push value. This would be super-useful for long range trips where gold minecart tracks aren't exactly usable, or for adding a bit of "mechanical" power to a creation, instead of the magical redstone "suddenly it's moving" situation.
I don't know how/if minecarts can be modded in, but it'd be pretty neat. Bonus points of they had two optional track pieces, a recharger and a launcher. When the launcher receives redstone input, it activates the minecart, and when it's lacking redstone it deactivates the minecart, allowing you to set up detector rails and delays so that you could easily dock and call upon your powered carts. Charging rails or some form of station would work similarly. When the minecart passes over it, it adds electrical charge. This could also be a block that you place beside the track, so that you could have your cart move into a launcher, which stops it in place, and ends up sitting right beside a charger block that quickly refills the battery. "substations" would be viable this way, by having the cart pause next to a small solar flower/batbox and recharge before resuming transit, allowing for truly massive and rather automatic railways.
I'm a fan of powered minecarts, but they never get enough love :<