This is a bit of a thought experiment I've been working on based on building a cube from the starting point of the Amonkhet Cartouches and Trials. I did my best to build this cube out with the implications of those cards in mind.
Enchantments Are Important
Auras especially!
The Trial mechanic allows for a lot of re-casting of enchantments
Implying enchantments that take the place of instants and sorceries (like the Omen cycle from THB, which have also been included!)
Removal Is Slow
Due to the Cartouches, I don't want to punish players for using the things the cube is built to do. Most all of the removal in the cube is kept at sorcery speed (though thats not to say there aren't any instant speed options).
Cartouche of Ambition has -1/-1 counters. Thus, no +1/+1 counters will be in the cube.
Lots of interesting space to explore with proliferate, removing counters, and Sagas!
Other Ideas
There is a minor Delirium subtheme, due to the abundance of enchantments making the card types easier to hit.
Persist creatures are in, but I don't want them going infinite, so free repeatable sacrifice is out.
Currently heavily multicolor. This is mostly because I don't have any set color pair themes. This may change in the future, especially to make room for some kind of dual lands.