That is pretty much in the game, it is called a "Off Power Rail". Does the same thing what the 'soon to be added' rail does. So, basicly Place down a power rail, then in a instant, you got a rail that does what you are thinking about. Though, the off power rail is much more strong on slowing down stuff.

According to the MC Wiki,

minecraft.gamepedia.comAn inactive powered rail will reduce the speed of a moving minecart, usually stopping it within one block's distance even on a downward-slanted track.

Though, it might be easy just to goto the nether and grab the soulsand, and place the track over it.

Or we can use a track that is made with soulsand, redstone, a rail, and a Slime_Piston.

Like in a shapeless pattern. Make it less expensive then it is right now, so it will be easy. Or in a fixed pattern like Rail, and redstone on top, and soulsand, and piston on the bottom. Easy. And this block should have lower intensity then the powered rail when slowing stuff down. All are ideas. (Off topic, but hearing a chicken swimming in lava, and making that hurt sound is annoying.)

Cool idea, I will consider making a mod for you like this if I can. If I do get around to doing it, I will PM you.