Well, I managed to do a little something - edit the inline Shader so it acts very much like what you would expect a "proper" selection to look like in an application:
It can also work with the thicker line we have had so far:
Feel free to comment on which one you would prefer.
That loss of opacity between objects with straight edges is a side effect of a C2 bug (I guess) that hopefully can get fixed.
More progress to come soon, hopefully.