Sounds very convenient, Sirena becoming available when Le Havre needs a new vessel.
To be honest I'm not sure what P&O would put on Hull - Zeebrugge to replace the Bruges and York. A conversion of freighters, perhaps Norsky and Norstream, along the lines of the Darwins, though not with such a high passenger cert. Two new freighters to fill the void left by Norsky and Norstream. Though they are now 15 years old so how viable a conversion would be is another matter.
Certainly my gut feeling is P&O wont be ordering anything along the lines of Bruges and York. The lock also causes limitations. Fuel efficiency is another matter, or another nail in the coffin. Stena pulled the plug on the Discovery for this reason.
On another note, I see Norman Leader, now Nova Star has finally arrived with her new owners. Only taken 4 years! I'm surprised Stena wasn't interested. I though she would have made a good replacement for Stena Europe, Epsilion, or Oscar Wilde. I heard she had build issues, but I'm guessing they have been ironed out.