well, one downside I can think of is that that decorative trim (hem-like) thing on the flat/top sheet that would normally be at the top/head end of the bed would end up at the bottom, right?......that might give me a bit of a "world turned upside down"-feel while sleeping??!!......also, my Mother was stickler for making sure the "top" of the flat/top sheet was facing down so, when pulled back at the top/head, that decorative hem/trim would face up with the neater sewing finish exposed.....
I also only sleep on one side of my queen-size bed, but don't rotate the sheets because, well,......(see above!)
however, the fitted/bottom sheet could definitely be rotated, it seems....