If they upgrade to bigger boats say 20% more than the current Spirit of Britain and France with new Prides of Dover and Calais to take advantage of the large new Port being built in Calais, it makes perfect sense dropping to four boats. The onboard service crew moved over to larger vessels would better support increased passengers numbers per vessel because no one likes seeing facilities cordoned off at peak periods. Losing Seniors Officers, Deck Crew and Engineers would be a loss of Quality jobs in East Kent fro. merging four boats into two but it will lower costs bringing maybe lower ticket prices. They could automate the booths at Dover and Calais for cars like the Tunnel did a few years back also to save money with API, physical staff is a bit wasteful in resource.
My only fear would be French Strikes and Bad weather because when that happens Dover gets really behind and with six boats P&O take a long time to get back to schedule and clear the backlog, with just four...?
The Seaway, Burgundy, Canterbury and Kent will be about 30 years old by the time these two new super ferries are built. Two had major upgrades to change Pathway and Highway from Freight only to what is now the Kent and Canterbury but after 30 years I could see Seaway and Burgundy going for scrap. Canterbury and Kent could be sold to Mediterranean operator or simply kept and moved on to less intensive routes as extra capacity or relief boats during maintenance of the regular fleet. The Seaway has only ever been Freight so I have never been on her but the Burgundy really has been the Rust bucket of the high seas for last decade, it actually pains me to see the woeful investment in that boat as taking my Wife and three young kids on her proved to be the longest 90 minutes of my life, tetanus running through my mind as the kids played in an excuse for a play area... Canterbury and Kent got their upgrades almost two decades ago so a journey on them is comfortable but feels like a supersize Cafeteria. This said all four of the boats had been built for DOV to ZEE run and a different era so for most of their life time they have been run on a route they had not been built to do and I commend P&O for their effort but it is time for these boats to move on and get a new product on the DOV to CAL run.
I live in Belgium now for almost 14 years and from start of Norfolkline (DFDS) new boats I became a Dunkirk only fanboy being a quieter Port, it was only the Britain and France that made me come back to P&O so if they want Passengers they have to invest. The Tunnel refuses to invest aside from upgrading terminal buildings, finding a functioning toilet on their trains when you have three kids is something that makes me avoid Eurotunnel and book the Boats as often as practical.
Clearly in a post Brexit world the capacity across the channel will need to be reviewed. DFDS ships originally did their run to Dunkirk in 90 minutes, today it has been changed to 120 to conserve fuel but if your loading more freight because of less capacity into Dover both P&O can speed up and do more per day as SeaFrance did.