I kind of hope there are no plans to do this, because it goes against what FFXI is.
It would replay what happened with Abysssea, it would wipe out many years and great effort into gear in one patch. This is very often a point more casual people quit because you effectively pull the rug out from under them.
However, if there are any plans at all to do this please do it via a simple upgrade mechanic and do not make all past gear obsolete.
Add a new form of XP from Abyssea v2 (I know you're working on it!) and allow all 119 gear to be upgraded to 120 via an NPC, when you trade the gear to it and it then asks for set amount of new xp points to upgrade (the best gear can have more complex upgrade requirements), make a cap per day so people don't burn it out in a week. This allows everyone to get to 120 (if you intend to do this) and keep all their gear.
FFXI isn't like many other games, players put up with gear wipes in other games for many reasons and those reasons to do not apply to FFXI.