Here's an idea - the cast modifier could work with more cast objects than just the Cube, sphere, and cylinder. There could be the field OB: and then you type in your existing object in your scene you want to cast to, casting that object to the object with the modifier.

I was doing some mechanical modeling when i thought it would be really nice for there to be an axis that can be created by the user (perhaps from one vertex to another vertex?). Along with the X, Y, and Z axis, a mesh or the selected verts could be scaled along this axis, moved along the axis, and rotated about this axis.
I would find this feature extremely useful because as of now, the only work-around to this is to rotate the whole model until it lines up with either the x y or z axis, do the work you need to get done, and rotate the object back to where it was.
It could be hidden, changed, or disabled at any time.