Could European Causeway not simply replace European Seaway (after modification of stern & cow catcher)? She is a freighter and replacing a freighter with a freighter shouldn't impact on passenger experience.
Regarding European Highlander, I imagine she could be centralised on just taking passengers with cars, focusing largely on freight. Naturally, berthing mods would be required.
P&O have worked very hard this past year. The dropping of Troon and the costly HSC Express, has allowed P&O to cut costs, also helped by the shorter crossing times and the more frugal nature of their ships vs the Superfast twins. However, like you said Steven, this goes completely out the window. Stena even market these new ships as the most efficient in the world!
If P&O moved the Highlander and Causeway to Dover, replaced them at Larne with vessels more frugal than their new Stena counterparts, then their ability to compete will be much better. However there is still the capacity increase - is this sustainable? Stena are going from 2000 to 3000, a large increase. To put this in perspective, Pride of Rotterdam has 3300 LM, and she can gobble up allot of freight.
It'll be interesting to see how Stena's running costs compare with Ulysses new running mate - Somehow, I see the Stena vessels having a considerable edge over their IF counterparts. The new IF vessels appears to have more decks = more weight = more fuel burn. Stena could theoretically replace both vessels at Dublin, and undercut Irish Ferries, like the scenario which P&O will surely experience at Larne.
I am a little sceptical of DP World offering P&O two new vessels for Larne, but if Highlander and Causeway could be shifted to Dover to replace Burgundy and Seaway, this could be an option. Remember, Seaway and Burgundy have had much tougher lives than their NI counterparts. The Japanese twins are in pretty good shape and if they were given a good dry-docking and refit (mechanically), they could easily operate out of Dover for 10 – 14 years.
I wonder would there be much of a demand (or if its possible) for a P&O Warrenpoint - Liverpool service? With the right ships could they restart a Fleetwood - Larne service?
I honestly don't see P&O investing in new builds for Larne over new builds for Dover tbh. Dover requires a highly optimised fleet in order to maintain the current schedule. Malo Seaways managed there of course (operating on the DFDS schedule). If P&O are that desperate to replace Seaway they could simply replace her with another freighter. If the Larne vessels were to go anywhere I'd imagine it would be converted to something similar to Nordica for the Dublin route. Even if they put the Mitsi's on the strait in the way you suggest, they'll still be down a (passenger) ship.
With regard to P&O operating a Warrenpoint to Fleetwood service, even if there was adequate space at Warrenpoint, Fleetwood is far from ideal. Its no secret that there were problems with the last ships to serve NI to Fleetwood and the tidal nature of the port (lack of dredging admittedly didn't help). Just like Preston I'd say Fleetwood's days as a port for ferries to NI are over, a victim of the growing size of the vessels themselves to stay competitive. The Stena F-Max design to operate into Fleetwood (with the economies of scale to make the route viable in the longer term) was extremely expensive to produce, not helped by the use of lightweight materials (necessary to get the draught down while having enough lane meterage). With the constraints of Fleetwood, any modern vessel will almost certainly need to be to a bespoke (and thus costly) design with limited use elsewhere. In any case, how would such an operation compete with the Heysham operations in terms of efficiency given the costly nature of the vessels?
So far as P&O bringing in new more efficient vessels for Larne, would that not be a race to the bottom? Stena have made much of the flexibility designed in to these new vessels - they are operating an overnight service to Birkenhead and a couple of hour long crossing to Cairnryan after all! Stena could simply follow suit and design even more efficient vessels themselves (easily done. For instance shrink the e-flexer design, or switch one of the 3 vehicle decks to passenger usage, or just remove it all together), moving the e-flexer's to any number of routes or the charter market. The current Larne vessels are already pretty efficient, and I understand are running on just 2 of their 4 engines. The difference is Stena will carry more freight and more passengers on the same vessels (but more efficiently than at present) than P&O can manage with their current port constraints.
You are right to point out vehicle deck capacity of the e-flexer design is much greater than the Superfast VII class. I can only think either: Stena foresee a large increase in traffic, may be considering reducing the number of return crossings, or that it is simply more cost effective to build a batch of exactly the same vessel even if it is too large - if the hull form is as optimised as it appears to be then would removing a freight deck that will otherwise be empty anyway make that much difference as opposed to redesigning the vessel? I suspect the latter may be the case, especially when there is scope to move the vessels elsewhere after a while - its a very Stena like thing to do and don't forget they have experience in shortening as well as lengthening vessels, especially when they were originally built to their own design. Personally I think the pax capacity of 927 is possibly a little tight for Cairnryan at peak, but then there is probably scope to convert cabins into passenger spaces for example to increase that number. Its early days yet and it will be over 2 years before any of the vessels arrive, so I'm sure more will become clear in the coming months and years. It isn't inconceivable that there could be design changes as well.
Hopefully Channel House is a flurry of activity at the moment as they come up with something to counter the threat!