I would say sell massive kits of all the basic minecraft blocks so people can make their own creations as if they were placing blocks in creative mode in-game. For actual project sets you could sponsor a new contest where players have to submit project designs to LEGO for manufacture. Winners get one of each set made.
First, I would like to see all the hostile Mobs and Passive Mobs in Lego/Minifigure Form. It would also be great to see an enderdragon. Possible sets could include: The End, The Nether, A forest, A desert, an ocean/body of water, dungeons,etc. Of course you must also add minecraft items/tools.
as a long time collector of lego the idea of minecraft lego is a sweet dream come true.. mod and player minifiguers would be a much welcomed addition to the sets... chest items perhaps? diamond, iron, gold ect would be amazing!!