This topic, like a few others, overlap with others..,
For example..,
AR Coins Have always become Unobtainable after the expansions .X series finishes.
in the one thread asking for a change to the Gear Drop(to remove the unneeded Role/Job RNG by converting to Head/Chest/Arm/Leg/Feet Coffers.) one of which was The AR Coins becoming something Akin to Tomestones.
<which would make older AR drops become Purchaseable like Crystals/allagan/etc crafting items, or individual pieces.

if it was in This form, I'd agree.
Since it reduces the Amount of Tabs and Coins in the Currency tab.<Since it would phase out with the current system, only those who kept old Currency would feel that pain of their own choice. Their Burden. Not anothers.>

To reward the players efforts.
And if they don't have enough to use their currency, a turn in/exchange should be set.
[For example, the Raids Exchange Items, if you don't have enough, you can exchange the remaining items for useful, or millable currency.]

TLDR:
While I get players hold onto Nostalgia and memories of past encounters.
There isn't much reason to hold onto items that don't serve a purpose. <even one person's bragging rights(even more so, if it was the single most peak object in-universe), is the world's ancient history>

The Rest Exist to reduce bloat, and also give a push/semblance of restart for all involved in current content.

These Currencies in the Tab are fine.
But Reduce them to a all encompassing Poetic.

We have no need for them all to be there.

And give old Currency a reason to be traded/turned in.

[Like I mentioned at the start, the topic overlaps in other systems. So Ultimate Totems Can be converted to something larger. Since you have no use for them if you no new job gets a version of it, and if ULT raiders get some gain from it, then no harm. <that in itself is another topic>
And excess totems for trials, or other content, can/should unlock a shop once you've reached enough to buy the mount and still no drop<potentially with other things to trade in for, for those unfortunate to get it last second, or have yet to get cards or bard mats>]
An Endless topic indeed.