Continuing from an older thread as it hasn't been addressed.
I keep having this issue of my sculpt moving away from the Mirror Plane and no amount of adjusting coordinates solves this.
It would be great to have the option of locking the Mirror Plane to the sculpt and also center the Mirror Plane to the center of the sculpt in case of accidental misalignment.
Being able to lock layers to the mirror plane would be very useful. Not sure if possible, but would be incredibly awesome if each layer had its own mirror plane, which could be auto-snapped to the central mirror plane's flat axis