We can speak a little bit from experience over the last twenty-some years or so. In the wheat field, I was given some numbers. Around only 2% of varieties have been deregistered during that period of time. This isn't a situation that has been identified as a problem to us in that way. You have the two regimes operating at the same time, variety registration and UPOV plant breeders' rights, and we just aren't seeing this issue.
On November 4th, 2014. See this statement in context.