Simple Idea, it's like the golden tracks, except replaced with diamonds, 1 recipe would give 16 of the tracks, and what makes them so special is the fact that they force the minecart forward with such a great amount of force, it goes very fast, and pushes any living thing (aside from the enderdragon) in the way aside dealing 2.5 hearts of damage. It would last for around 100 blocks.
It's not exactly something somebody would waste diamonds on... perhaps having them being able to curve would give it an advantage, but otherwise I can't see a use for it.
Powered Rails go on for 75 blocks-ish
fixed
better?