From experience, I know it is a compromise for both sets of speakers.
Bass not be as tight on both sets, imaging and soundstage will not be as good.
But if you do it, make sure you stagger them, so each pair has an inside and an outside speaker. Chances are, that the optimum position for both sets of speakers in the same room, will be very close. If you put one pair inside the other pair, one pair will be more compromised than the other. At least if you stagger them, their distance away from each other will be the same.
Bass not be as tight on both sets, imaging and soundstage will not be as good.
But if you do it, make sure you stagger them, so each pair has an inside and an outside speaker. Chances are, that the optimum position for both sets of speakers in the same room, will be very close. If you put one pair inside the other pair, one pair will be more compromised than the other. At least if you stagger them, their distance away from each other will be the same.