Would it break anything to add an Opportunity Attack when a prone creature stands up?

@yesirote @JeremyECrawford would it break anything to add an Opportunity Attack when a prone creature stands up?it might – we're a little more liberal with stuff that makes people prone knowing it doesn't provoke

— Mike Mearls (@mikemearls) April 27, 2016

@yesirote @JeremyECrawford if anyone in the party has an at-will knock prone, then definitely will break stuff

— Mike Mearls (@mikemearls) April 27, 2016