Hello Andrew,
I'm using this for a week now in ReTopo, but I'm not convinced about the improvment. While I like better capturing, RMB seems to me not consistent, RMB resizes the brush, moves points or makes quads depending on the brush size and brush position: it doesn't work always the same. I understand the intension, but in this case it's a bit of an overload of the RMB (IMO): it breaks fast interaction routines and automatisms. For me it's not convenient having to resize brushes to switch between the functions of "moving vertices" and "making quads". I sense other faster possibilities with other keys and mouse buttons and less interrupting workflow. Still close to what it is now but less interuptive.
Another one: while hovering over the retopo mesh it is currently not possible with RMB to change brushsize. User must find an uncovered spot of the reference mesh to change brush size. Or alternatively use the brush slider in the GUI (usable but not convenient) or scrollwheel/touchstrip (to slow, not stepless).
Best regards.