Something that has been on my mind for quite some time, and that I would consider learning to mod just to make it happen would be discretizing the potion and enchantment system. By that I mean that instead of having the ability of making potions that restore 50 health, 51, 52, etc., depending on how high your alchemy, you would only have discrete values, eg. 25, 50, 75, 100, 125..., or whatever you choose, and you jump from one to the next instead of going through all the intermediate integer values.
That would avoid a lot of inventory clutter that you get from making potions and leveling alchemy in the process. I remember I've seen a mod that does this once, but it didn't seem very active and updated.
There were a couple of cards that I submitted to the custom cards subreddit that were later printed almost exactly like I posted them. I mostly remember Foundation Breaker (mine was 2GG cost and 3/2) and Damn (mine was 1BB // 3WW for the costs)