I disagree with a lot of your picks for a few reasons. In my opinion, this game mode is going to relate to Guild Wars's Jade Quarry PVP where players capture strategic points and effectively, race turtles to return resources back to their base. Capturing objectives provides resources for turtles to carry, and side objectives with archers to attack enemies and enemy turtles help your cause.
For those who have played the game and want to point out the flaws in the analogy, I admit it isn't perfect. In the Guild Wars map, nuking minions is what scores you capture points which doesn't apply here.
With that in mind, I predict the strongest champions will definitely be those with fast movement speed, sustainability, and high damage output. This means that Tanky DPS champions will definitely be at the top of the list while slow, squishy characters will probably be closer to the bottom even though they have high damage output. The metagame strategy will determine this, but the effectiveness of 1v1 champions and assassins will depend on how often people focus on moving in groups as opposed to splitting up to capture objectives.
Because of this, I think a few of your picks are very much off. Trundle and Garen should definitely prove to be great characters. Garen is tanky and can have huge damage output at early levels with his spin. Trundle has decent survivability, but he is also almost immune to CC with Merc's and has solid damage output and great movement control.
On the other hand, Anivia, being super slow and requiring a lot of time to farm will probably be a poor choice for this map mode. I'm not sure how many supports will do, but Janna with her ability to move enemies capturing points, heal her whole team, and boost movement speed will be great.