Im not sure why NOLA keeps getting brought up. There's no way they are going to jump to an Excel ship without trying a Dream or Vista class there first. It makes no sense!
I think it's fairly obvious where the 2 new excel are going. PC and Miami and don't be surprised if they take another play from the RC playbook and one of these ships is built specifically for short cruises to Celebration key. But the main point is, they'll be going to those ports so 1 excel at each port is on short cruise rotations.
Unless Carnival transfers Venezia and Firenze back to Costa come 27/28 I also can't seen an Excel going to NYC. Those 2 ships won't really work anywhere else than where they currently are, well perhaps Virginia?
Here's my prediction, im not using ship names because I think we'll see a bunch of rotations before or about the time Excel#4 joins the fleet.
2027
Miami
2x Excel Class
1x Vista Class
1x Conquest Class
Dream class moves to Virginia OR NOLA and Conquest class moves up to Virginia.
Sunshine is Retired.
2028
PC
2x Excel Class
1x Dream or Vista Class
1x Conquest Class
1 Conquest class from PC replaces the spirit class vessel in Galveston. The Spirit class vessel will go to either Tampa or JAX to replace a retiring Fantasy vessel.
Galveston 2028
1x Excel
1x Dream
1x Vista or Dream
1x Conquest