I envision that it does not matter, because this is a tactic that would 1) be available to all, and 2) it gives up your vote for someone of your own party, thereby weakening your own position. It's self regulating.

Can't they do that now? If I think my chosen primary guy is winning in a landslide I could just register for another party I don't like and vote for someone who I think is easier to beat.