I kind of doubt it. Back when Royal was building ships like you are discussing they didn't own Celebrity or SS. They bought X in what...'97? And SS just a few years ago.
So they were already building out and planning Voyager and Radiance class while they absorbed X, which was a very small line at the time.
Fast forward to today... The company now has a significant fleet of X ships with more coming. If cruisers are interested in that type of product RCG already offers it.
Little reason for them to cannibalize sales from X rather than just building more X ships to service demand for those itineraries. Most brands don't attempt to be everything to everyone. Just like Carnival and Princess cater to different demos under the same parent company.