Idea I had, which I will not be modding, because, well, look how frequently ASCII Zombies gets updated (FTR, I apologise to the players of ASCII Zombies).
Anyway, basically, I think it would be really cool to do TCGs here. Prospective mods would post the TCG they wanted to run, and any special rulesets, and players would have to submit a copy of their deck to the mod. The mod would then assign each card a number and use random.org to determine how the deck is ordered using the sequence generator. Each shuffle would result in a new sequence, with cards in the graveyard/hand/field being removed from the list and the list being renumbered.
The mod would also be the ultimate authority in what is and isn't legal.
Images of cards could be used to make playing fields if the players/mods so desire.
This is a fairly mod-intensive playstyle, so please only mod games in this style if you won't do what I did to the ASCII Zombies players.