I had this same concept on a website called 2kMTCentral (NBA 2K's version of MutGG that fell off) and it was planned to be implemented but I do not think it had the facilities to do so. With a website like MutGG, I believe there is a strong enough team to make this concept a reality.
The concept is a trading card PvP-style game that involves opening packs and using card stats to compete against other opponents. You open packs to get more cards (cards get added as the cards in Madden get updated) using "GGCoins". "GGCoins" is the currency for the game and it is not purchasable and can only be gathered through playing the game, either singleplayer or multiplayer. You can also obtain players by using the auction house (it is understandable if this isn't possible).
Game Concept: You play either a computer or another opponent in the game. There will be seven total rounds and best-of-3 overtime in the event of a tie. For every round, a wheel will be spun for the position group that you will need to choose from (QB, HB/WR/TE, OL, DB, LB, DL, K/P). From there, both players would pick their card of choice and lock them in. Another wheel is spun choosing what specific stat is chosen (Break Tackle, Speed, Pass Block Finesse, etc.). Whoever wins the round gets a point. If there is a tie of the stat, they have to choose another card and the wheel will spin again. Whoever ends up with more wins in the seven rounds or the overtime is the victor. You receive GGCoins based on the number of rounds won and the winner receives a small boost.
Starting the Game: Every player would receive a 'Starter-Pack' which would include two 80-82 offensive and defensive players (four total). The rest of the team would be compiled of random silvers and golds (every player receiving the same amount of both). You start with a base amount of GGCoins which can start you off with a pack or you can save.
Game Modes: I believe that there would be a casual and competitive standard for the game. Casual does not have much to it besides just queueing for a match, playing it, and receiving the awards. The competitive mode will be different than the MUT mode. Instead of playing up to the Super Bowl, you go up tiers based on win totals, receiving rewards as you go. The amount of GGCoins you make goes up as you go through tiers, allowing you to open better packs more frequently. You only play people who are in your tier and there could potentially be a max/min overall cap based on the specific tier to prevent players from dominating far inferior opponents.
Along with the two standard modes, there could be another mode where you face others in much shorter games (3 or 5 rounds). These games would be less competitive but faster to go through.
One final mode that I think would be great to add would be a draft mode. You pick 24 players and you face off against other players that have drafted. The reward for this mode would be a draft board with 3-4 different tiers. These tiers are based on playing the game and the only way to go up one tier to the next would be to clear the previous board. Once completing the final draft board, you go back to the initial board. You can reset drafts, but there is an entry fee of GGCoins for each draft (the first draft is free). These drafts would also update after each promo, potentially having a 'captain' round of one elite from the latest promo.
Event Modes: Similar to a House Rules mode, there are random event modes that would pop in once in a while (Offense Only, Defense Only, Wildcard Rounds, etc.) that would give you special rewards based on win totals in that event.
Training/Power-Ups: I'm not sure what to do with training and powering cards up.
Theme Teams/Strategy Cards: TT and Strategies would give boosts to players just like they would in MUT.
Abilities/X-Factors: Abilities and X-Factors will only help players' stats boost if they are added into the game. For example, the best RB in the NFL Nick Chubb gets Ankle Breaker, which increases his Juke Move and Spin Move by +3. If you put the Bulldozer ability on him, he receives +1 or 2 trucking. Doing this would help the variability of each players' cards and would make the game less predictable.
Feel free to ask any questions about the concept and let me know what you guys think about this.
