3d Print -> Rotate/align to XY plane help

I could use some help with this patch:

Preferably, a way of handling the rotation without changing the current view.

As it is, it requires a Face selected in edit mode – such a workflow seems strange for Blender’s normal use, so I didn’t try to add this as a core Object → Transform feature, but that might be something good for the future if anyone has ideas on how that should function.

I think 3point alignment task is different from printing job.