What I think goes on is that although any broad beam, broad stern boat like a mini wants to go at an angle to centerline when heeled, it is not allowed to because the keel/ dagger board are parallel to the centerline. If the boat has 2 dagger boards, one on each side that are at an angle then I think the boat would sail with less resistance. This though would cause a problem with the keel direction. You could turn the keel as you suggest although that would be making an already complicated mechanism that cants and slides even more complicated. When the boat is sailing in a breeze with the keel canted, the keel would be added hydrodynamic stability with the canted keel angled downward by the same amount as the dagger board is off centerline. This would be a good thing if the angle was not too great. 7 degrees might be too much for optimum lift / drag of the keel. You would then have the problem that in light air with the keel not canted or even canted to leeward, the keel and the dagger board would be fighting each other. You would also have this problem reaching in light air and running in most conditions. If you could design the boat so you did not use the dagger boards in these conditions it might work.