Here's my general take on things: KOTH with a laterally-moving cart was confusing and gimmicky in Namicott, and this map doesn't improve on the concept. When TF2 players see a cart moving on a mine track, they've been conditioned to assume there's some gameplay significance to its movement and that at least one team can have some effect on it. Just like when they see a metal pad they assume they're meant to stand on it, and when they see a briefcase they assume they're meant to pick it up. Every time Valve has introduced a new gamemode, they haven't messed with these fundamentals. And they especially haven't done so as a "fix" for a standard map whose layout wasn't working out.
You bring up some great points. There's several things I want to assess (including ones you mentioned) to do with the mode, but I'm willing to play around a lot. One of the big issues as you say is that the way people move around the map changes completely, and I've definitely noticed that since I made the CP move, people do stick to the 'cart'. There are advantages to standing by the cart, being dispenser healing from the cart and blocking it from attackers.
I'm having fun playing about with this mode, and I'm certainly going to try a few more ideas before just settling, for instance:
- Having the cart tick down clocks only when people are within the cart range
- Having the cart tick down clocks at double speed when the owners are within the cart range
- Going far out and making it sort of tug-of-war (but that would be an idea for a PL map with KotH elements rather than a KotH map with PL elements)
- Playing about with the aesthetics of the cart so it's appeared as more of a landmark and less of a payload cart
- As some suggested, try having either side of the map as a 'finish' point
- Having another go with single-timer KotH and having the payload go down the hill to the end, where at the end of the time it falls off the cliff
I'm also spitballing a concept based on the last idea:
The cart moves at an incredibly slow pace from the top. When it reaches the bottom, whichever team owns it wins. Re-capping pushes the cart back up quite a bit to solve the issue of letting the enemy hold the point then rushing out. Both timers still work normally, victory is achieved by either: Reaching the bottom of the hill, or having your timer run out.