The idea is that when a locomotive passes the this track it will be tagged as "ready to link up" so when it touches a cart it will automatically link up with it. This is useful for when your at the end of the line, and you want a locomotive to reverse into the cart and then link its self up. I think this track would be even more useful if it then put the locomotive into the slowest forward speed after it has linked. So this track would mainly be used as a for shunting yards. Because currently dead end sidings are quite a pain, and are pretty much useless without the ability to automatically link up and then go forward.

I already have this being worked on, and am testing it currently.

The main problem with the Coupler Track is that both carts must pass over it. However, I'd be ok with a new Coupler Track Mode that causes any Train that runs over to couple to the next Cart it collides with. Also a new hotkey would be nice as well.

Actually implementing this would require editing MinecartHooks to look for a flag on the train saying its in couple mode and then respond by coupling the carts when colliding (with some checks for safe relative velocities). And it would require modifying the Coupler Track support modes similar to the Locking Track.

Yeah that's one problem I noticed, even if you did manage to set up a system you'd only be able to have a set amount of carts. And I believe it's just more complicated than it's worth, hence people just use the old loop method.

Adding a track doesn't solve the fact that you still need space for the train. There is always going to be an upper limit.

You can already do this with some problem solving using the current tracks.

Here's an example: http://imgur.com/bRolJeD
Locomotive comes in from the bottom right with no carts, gets put in reverse by top left limiter track, backs onto coupler tracks and links to carts, keeps backing onto limiter tracks and gets set to forward again, leaves with carts.

My idea was a similar layout to that, the problem I found was that it didn't support different cart lengths, like it could be designed for 3, but what if you had a train come in with 5? Unless that design does it perfectly?

That shouldn't matter as long as there is enough space for the length you need, in section 1 to clear the switch before the train is reversed and in section 2 for the locomotive to reach the limiter track before the back hits the buffer track.

Here, have a video:
https://youtu.be/PJ-lb1jYtXM - Railcraft [Episode 1] - Backing Up To Couple

Space is still limited by the space between the switches.

Here's how to do that with current tools:
https://youtu.be/0jBVU8vOgkQ - Railcraft [Episode 2] - Turning Around

I think it could, I may be wrong but here's a concept video showing the new track on my test client.
https://www.youtube.com/watch?v=Zaxqc7XZ3P8

I'd say it is necessary to sort of trains that have reached the end of the line, but may need a few adjustments.