About a year ago the upgrade on the 7 night Fantasy cruise from a Cat 4 to the Cat R was just over $10,000. About $4,000 from the Cat 4 to the 1 Br. So an estimate from the 1Br to the Royal would be between $4-5,000 and that is in line with what I have heard reported.
We were watching the one open Cat R on a January cruise since it was still open. Talked to the hotel director during the cruise and someone grabbed it at 11:35 the night before the cruise. So people will still make the switch last minute and pay full price.