Most shapes we make have some sort of symmetry. Mirror does not help much. We need live symmetry. Consider this: Draw a curve, create lofts to build surfaces and mirror them. Now you invariably need to modify those curves to fine tune, and the symmetry is gone! Delete the mirrored object and re-mirror the whole thing. Get the picture? (Unless I am missing something).

Yes this or a soft mirror (just visual mirror but with no real geometry, like Catia freestyle

We DESPERATELY need this

This is HUGE -- the mirroring tool is awkward at best (for me)

I would love to see this with G1 G2 over the mirrored edge. (Something like the Mirror Modifier in Blender ? )

This would be a game changer. yes please!

This will help when modeling things like helmets

Or at least have something like instance duplicate that you can mirror without welding it

Support for Radial Symmetry would be also welcome :)