Did the 'Endeavour' get fins. I'm not 100% sure, its possible she did get them when she received the twin deck loading set up for Dover to Calais, back in 2008. She is going in for 20+ days for refit shortly, not sure what she is having done, probably a repaint, but internally she might be getting some work to bring her more in line with P&O Ferries fleet. Perhaps she is getting Wifi, International Food Court (Highlander and Causeway got one last year), and maybe a Club Lounge (upper lounge, just below bridge would be ideal and given the 7 hours would be popular).
Norbank and Norbay could do with a major refit. Clean and comfortable they are, but they are still very much North Sea Ferries, and now they are 20, and feel a little dated. I think its time they had their mid-life internal refit. Perhaps along the lines of Stena Mersey or Cotentin. Certainly would do the route, and ships justice.
I think your right about the 'Seaway' being pulled apart, given P&O have all three sisters under their flag, and their 20+ and clocked up nearly as many miles as the 'Chunnel Beaters', it would be a good idea if they scrapped her for parts to keep the sisters going.