I agree on the French run. When she was with P&O, the latter said she wasn't viable to run on Dublin to Cherbourg because of her fuel efficiency, despite her popularity.
I wouldn't rule her out on the Holyhead to Dublin route. If Nordica is laid up, and their is demand for a third ship, then she would definitely be a good option. It all depends on numbers (which I hear are good), and naturally berthing slots. Superfast X, which is an improvement on the Nordica in many respects, has provided no improvement with regard to freight capacity.
P&O I imagine will be sending European Endeavour off for refit soon, I suspect February / March. Stena Nordica could possibly be chartered in to cover EE's time table. Bearing in mind it would only be a temporary arrangement, it could happen. DFDS chartered the European Endeavour from P&O to cover Birkenhead to Dublin, in direct competition with P&O's route, so anything is possible.