When I hit "mirror X" on object with supports then I think that object with supports will be mirrored. Now mirror is not mirroring supports. I thinks it`s bad becouse If I needs simetrical prints then I need rebuild whole supports structure once again. It`s waste of user time.
I would also add my vote to this feature request. If the Mesh > Mirror Mesh command also mirrored the associated support structures, this would halve the time to create the custom supports I often need to generate when working with paired symmetric models - which I work with extensively. For the things I do, the automated support generation tends to produce suboptimal support structures so usually I have to create custom supports. The Edit > Duplicate Models command does a good job of copying the suppports, but if I then mirror the copied model, the support structures remain unchanged.