I'm currently downloading and trying models and noticed that many of them are standing upwards, that is rotated by 90° on the X axis.
No doubt this is to have less support structures and thus having less ugly spots on the final result. (Also saving filament and space on the bed.)
However, so far I always rotate it 90° so it sits flat on the surface. It's not big deal to manually enter 90 every time, but a quick button to rotate by 90° (multiple times if necessary) would be handy.
Come to think of it - maybe it'd be easier to just enhance the slider? Put it markings at every 90° and make them a hotspot, so you can easily click on the angle you want?