Basically just that. I was copy pasting an asset I had just made and noticed I cannot seemingly rotate it sideways onto its side. I can rotate it on the X axis, spinning it around the tile, but I cannot turn it sideways without rebuilding it by scratch. I wouldn't even think to go so far as to add partial rotations to the Y axis because it would make for more complicated code. I think 90' turns would suffice, same as the ones it does for the X axis.
While probably not a super hard feature to add, It doesn't take super long to remake an asset turned on its side with how fast model making goes in this software, so it's not super pressing, just a QOL thing to request that saves time.