I know that the upcoming game Dungeon Lands is already doing this but since its a totally different game and it might work well, why not a DM mode for Card Hunter where one player acts as the GM and controls the monsters ? And not just in a single battle but the whole dungeon/quest, it'd just be a mode for fun so no one would abuse it for rewards, maybe unlock the ability to create your own dungeons. You'd just host your map and wait for a foolish adventurer to join.
Bwee hee hee! I get to quote myself referencing myself quoting myself! . . . Or let me not do that. Here is the most straightforward answer to your prompt: We'd tried to answer this before, you see. That doesn't stop it from being a valid question, of course, with all of those older threads off the front page. It looks like people really wanna be the Dungeon Master.
Sounds like a tasty premium feature or something unlocked. Since its card based it would just make sense that you could find and trade monster cards themselves for the purpose of using them in DM settings. Then they could also sell all kinds of DM accessories for building maps, unique furniture's and such.
I had a similar but different idea not long ago. I think it would be neat to unlock a challenge mode where you control the monsters while a team of adventurers (controlled by Game Master Gary) attempt to defeat you. Similar to the Plants vs. Zombies game mode where you control the zombies and attempt to get past the cardboard cutouts of the plants. The monsters you control and their decks are pre-determined and the scenarios are difficult (due to lack of player-controlled customization of the decks) so it's more a matter of mastering the scenario than building a deck. I imagine this would be fairly easy to code as the monsters will probably all have their own decks coded in the game. So we'd essentially just be switching sides with Gary for a challenge.