Cheers for the feedback Mark! I'm glad to hear that you're getting on well with the cut detection rules.
And as you have said the curbs do decent job of preventing cutting, and occasionally slowing the car down which in turn also deters cutting.
Regarding the white line at the pit exit, since I am unsure as to whether you are referring to the one on the right as you exit the pit lane, or the line on the left as you enter the track, I shall provide a response about both. The white line at the end of the pit lane, on the right hand side, can be cut since it is not really possible to gain time at this point when you are exiting the pits. As for the pit exit line, as you enter the track, it is also possible to "cut" here given that there is nothing implemented in the game to prevent or deter a car from entering the track sooner than it should, and there is no real time to be gained by doing this either. However, if there is an incident at this point on the track, caused by a car exiting the pits and crossing the white line, then a drive-through penalty will be issued by Race Control.
Yes, this is possible - please see my response above.