I can't find it and searching for it brought up way too many posts but I vaguely remember a dev post saying the Armoire is a vestige from 1.0, including its coding, so a lot of new items won't be able to be stored unless they're related to previous events. But then they made it so items like the Master rings can be stored and I don't remember those from 1.0 but it's been a long time.

Assuming they don't come out and say they expect us to buy new retainers (which they better not), it is likely we'll get new storage options to accommodate the newer items. But it's unlikely the majority of the non-unique/non-tradable items will be able to be stored since you can use them on the Market Board. Just be careful what we wish for; you should see how many different systems are in place in FFXI to store items because of how creative they had to get to get around the memory/storage issues. NPCs, key items, vouchers, etc etc. Items all over the place.