Celebrity currently has 4 ships in Europe. A larger ship might be able to do the work of 2 smaller ships that it currently has there - the Century and the Galaxy. That would then free up 2 smaller ships for more exotic and costlier itineraries.
That's an interesting option, but I really don't foresee it. The demand for cruises to Europe is growing, so there's little doubt that Celebrity Cruises will expand capacity there rather than consolidating capacity on fewer vessels. It's far more likely that Celebrity will shuffle vessels with GTS Millennium and GTS Constellation taking over the itineraries currently operated by MV Galaxy and MV Century as the newbuilds take over the itineraries currently operated by MV Millennium and MV Constellation. Either MV Galaxy or MV Century probably would take over the Bermuda itineraries from MV Zenith, which would either open new itineraries or leave the Celebrity fleet.
It seems very likely that the new class of ships will grow to more than just the two vessels (one firm order and one option) in the original contract. A couple vessels of this class probably will go to the Pacific Ocean sooner or later to operate Alaska itineraries in the summer and either Hawaii or South America itineraries in the winter.