Sorry for my double post...
I tried to study retopo tool for these days.
So I hope these feature like bellow.
1. On/Off switch for Stickiness
I realy love this feature that stick to original mesh (or VS model)
But when use retopo tool for a little complex model, It happen unanticipated reaction.
When I use "splitte" or drag vertex with RMB, the vertex jump to unexpected face...
So in this case, I think If I can turn off the sticikiness.
2. Stick to center of symmetrical line
With symmetry on, and I want to create a polygon near around symmetrical line.
Always I have to create vertex over the symmetrical line.
And after createing polygons. It looks as symmetrical, center splitted model.
But the position of these vertex is still kept as original position(where "over symmetrical line")
So when I want to move these vertex, or split the edge contain these vertex,
I have to search out these hidden vertex or edge.
So I think it is good idea for a new feature that,
when symmetry on, New created vertex force to stick to symmetrical center line.