I was waitlisted in Round 4 last year. I believe they only go to the waitlist if the yield out of Round 4 is lower than expected. I didn't hear of anybody making it off the Round 4 waitlist last year. Basically you either voluntarily drop off the waitlist or you hold on and hope for a low Round 4 yield. I waited until late June until I dropped off the waitlist and ended up applying EA this year. Also, Round 4 waitlists are not deferred to EA next year. If you don't get off the waitlist before classes start, your application dies, and you have to start fresh next season.
Also, I don't know how the Ad Com makes their selections from the waitlist, but I do know that the applicants that have made it very clear in their application that they will definitely attend Kenan-Flagler if accepted, are going to get the first nod.
Best of luck over the next few weeks. If you don't get pulled off the waitlist, I know for a fact that Kenan-Flagler looks very highly upon re-applicants. And don't be discouraged by a Round 4 waitlist, I have been told that 90-95% of the class is filled prior to Round 4.