More Robust CAD-style Inferences with Measuring tool (and constraint snaps)

The measure tool currently just measures a distance from A->B, but there is no hover/infer functionality like in standard CAD packages. Using the 3D cursor to establish before-hand the point in space I want to measure to is clunky at best.

Also, there's no real obvious way I know I'm measuring from EXACTLY the point I want to snap at the start, like a vertex. Easier ways to snap to midpoints and other elements of interest a plus too.

Also options for angle/axis/increment constraints.