Powered rails as a speed limiter

I've been playing survival mode with the minecart experiments on, and I'm actually pretty fond of the changes made!

My number 1 issue with the experiments, is that I've felt that the speed of the minecarts is a bit tough to control. Minecart maximum speeds that felt fun for transportation, like 30+ blocks per second, felt pretty tough to control for redstone builds, especially builds that deal with objects like hopper and storage carts, that change their physics once filled with items. I've made chest unloaders with sloped detector rails and fence gates,  but just one powered rails to help the cart up a slope can lead to so much momentum that a filled hopper minecart goes flying over or through the walls.

For solving this problem, rather than adding a new rail type, I propose that facing a comparator into a powered rail would make the powered rail speed up or slow down the minecart to a desired speed. You'd have much more dynamic control over the minecart than you would with a new rail type. For example, powering the rails with a signal strength of 1 would speed it up to a limit of 1/16th of the maximum speed value.

Imagine creating an adjustable speed-limit for your transport stations, or using it to let you slow down a minecart to decide whether to make a turn at a junction, or a shooting gallery. Simulating various engine classes for minecart races. Various speeds for moving platforms with Happy Ghasts. etc, etc.