Implements with just one hydraulic hose?

[SwingOak]

I have a Kuhn rotary rake and H&S four rotor tedder that both have a single hydraulic line. Power up, gravity down. Works just fine. Connect to whichever side of your rear remote that makes sense to you when working the lever. It's no problem.

 

[SmallChange]

Take a look at most tractors - lift arms on 3 point hitches are generally single acting.

Somewhere here I posted a question about whether any tractor 3PTs had downforce. There were a lot of replies with examples.
But your point is well taken, they are very much the exception. Most absolutely ARE single acting.
I like the idea of being able to lift the rears that easily. I certainly use my FEL to lift the fronts, for example when dealing with chains. My old machine did not have power steering, and I learned to lift the fronts with the dozer blade to spin the steering wheel when maneuvering in tight quarters.