i had a few shower thoughts and became very motivated to snap out a list of rules for an UNO + magic the gathering format combination using what we have in Tabletop Simulator.
there are a lot of weird parallels, between the colors, the number of board regions and their purpose, the average hand size... but the main conflict of interest is that it's generally good to have a lot of cards in your hand in Magic, but the opposite is true in UNO. so the rules have to be bent pretty awkwardly.
in general, i started with a flexible Magic format and wrote formal modifications to that format that bent the game into UNO's rules as well. i think it works better than it has any right to! but it's definitely still an absurdly long game with no obvious conclusion, unlike most Magic games. some slight changes have definitely got to make more sense, and i'm going to figure it out.