Pretending that my dslr was really a 6x6 in drag, I tried to see the square world within a rectangle. Not the easiest or most comfortable experiment - a bit of a test of patience, in fact.
I rather suspect that reverting to that format (6x6) would be a little less instinctive than I had thought. Okay with people portraits - probably perfect, in fact, but a bit more demanding in the great outdoors where so much intrudes and should be cropped away... I guess that explains a lot of the beautiful motifs that regular 6x6 devotees adopt: they get used to a way of finding things that work and avoid impossible challenges.