here is mine!

1 I suggest creating a sort of "olympiad" or a "decathlon" of games.
users compete on different activities, blackjack, roulette, slots, video poker, mines etc and the winner is chosen from those who are able to achieve certain triggers in all games in the shortest time possible!

2 trivia! general knowledge questions / bitcoin theme give bonuses to players who are active in chat and provide the right question.

3 happy hour. at a certain random moment of the day, the possibility of playing some games with cashback/loss back promotions is offered.

4 insert a "points" system . every mbtc played allows you to get points that can be redeemed for cash prizes or physical prizes (gadgets / amazon vouchers etc)

5 head to head game. why gamble/play against bj admin? create match between players. it would be fun have a blackjack game between two random players (of course a percentage from each game is provided to admin...)