I know the story arc for Abyssea is over, however given just how popular it has been, how many players it has brought back AND how many people bought 2nd accounts to play both chars on this content it would be kinda silly not to add more Abyssea type zones.
A lot of serious XI players now have bought, leveled and continue to pay for unique subs on alt accounts. This is mainly due to Abyssea type content where atmas make using 2 chars at once a decent prospect. Although it would be good to see more difficult party/alliance content I think it would be a big mistake to not add more of this type of Abyssea stuff and indeed not see it as the most important part of current FFXI(people will cancel these alt accounts if there is no further reason for them) and most content hardcore players like will be a turnoff to almost everyone else.
In a game with lilmited appeal to new gamers it makes sense to not lose on all these additional subscriptions players are going into, there is plenty of room for new Abyssea copy zones. If number of zones is a problem remake certain useless zones into Aby ones.
So yeah Abyssea is the most important content for everyone and looking at the next 12 month content I think it will continue to be, not expanding on Abyssea I think will be a big mistake.