It is possible that someone already booked in Concierge (or Category 4 Guarantee) will be moved up, but more likely that DCL will leave the suite available for people to upgrade into for a cost at the port.
Highly unlikely unless for some reason they are in a situation where they became oversold (possible cabins out of service unexpectedly) and, as the other poster mentioned, they will most likely upgrade the next highest rate to that suite. I wouldn't count on booking an inside cabin and getting an upgrade to the Royal Suite.
GET UP TO A $1000 SHIPBOARD CREDIT AND AN EXCLUSIVE GIFT!
If you make your Disney Cruise Line reservation with Dreams Unlimited Travel you’ll receive these incredible shipboard credits to spend on your cruise!