The idea to show boxes where the cursor hovers seems to be taken from the traindispatcher, am I right?
I have now developed a way to do just that, but there are still some details to figure out. However, the box will show on any grid no matter what is in there. Also, it will work for the editor (the trackbuilder does not have it!)
As far as the locked switches are concerned - I haven't made up my mind yet. I know at least for user-locked switches they're made quite noticeable in real life prototypes, but especially for slip switches it can be quite crowded, since you have two switch motors and thus two user-locks in one grid element, which operate independently.