Minecart feedback and suggested changes (full makeover)

This would take time, but IMO it's the best solution to solving minecart speeds:

Give all the minecarts the same feature as a furnace minecart, and then differ speed duration based on the type of fuel that is in.

The normal max speed still being 8 blocks per second: Lava applying a 0.5x to the speed for basically 3 hours (slowness matters too) Coal being just 1x for 15 minutes, Coal Blocks being the same 1x but for 2 hours. Kelp Blocks being 2x for an hour, and rare fuels like jukeboxes being up to 10x for an hour.

Rework powered rails to square the multiplier when turned on, but take the squareroot when turned off. And if speeds needs to change, just use another fuel type for instant replacement.

From the examples, lava would be 0.25x, jukeboxes being 100x while the rails are powered. Unpowered rail would give roughly 0.7x for lava and 3x for jukeboxes. It would rely on gathering fuels, but in exchange you would have a massive range of speeds.

You would FOREVER solve minecart speeds. People can make actual rollercoasters with reliable mechanics. Technical players can design with any speed they want. All the unused fuel sources suddenly get a use. (Wooden tools could become VERY interesting.) And whenever it needs balancing, its just tweaking some numbers. Its maximal customisation with minor tedium for players.

As for furnace minecarts? Who knows, maybe just keep current functionality but double the duration of fuels on use.