This seed is still growing...
Witness, the third and likely final cube I will burn my days designing: a cube consistent entirely of Universes Beyond cards. At time of writing (apr 11, 2024) there likely isn't enough cards to fulfill this requirement, but I'll get some foundations set up now to save myself the hardship in the long run.
I also have a goofy idea I want to note now: basic lands will be draftable, and tapped, common dual lands of your choice will be provided after the draft. This encourages triple color, but lacking basics will make you susceptible to modern land destruction. Time will tell if this is a good idea.
Rules: