The new tax doesn't make the move impossible but its not a red herring either, it could definitely have an impact. Without the new tax they'd likely have been able to lure him their for £70k or so, with it that would now be a significant pay cut, they'll probably have to give him £150k+ instead. Its not a wage you'd think is out of their reach normally, but its significantly higher than they would normally have to pay. Also their's the fact that their costs will have already sky rocketed from the effect on the new tax on current playing staff (its going to be paid retroactively for 2013 season). They have to manage costs to some degree or Champions League Football won't be a lure at all because they'll be banned from it.
We will see how FFP plays out.
Plenty of clubs will be breach of it so it depends on Uefa and how stringent they will be.
Either way PSG Come and we say goodbye to Cabaye. We've got no interest in competing with them on any front sadly.