I understand that part of the intent of currency caps is to encourage spending rather than hoarding, and to prevent players from having very large amounts of certain currencies when a new level cap is introduced or when a special discount or other temporary opportunity is presented. For example, end-game players would love to have extremely large amounts of Embers saved to use to immediately gear up all their characters the moment they reach the new level cap (which many will do within an hour because of the ability to take advantage of the XP boosts and the Mission/quest system). For another, I would have saved up a lot more than 10,000 Embers to use this past weekend during the +20% VXP event for the Embers-to-VXP quests if that had been possible.
However, there are caps which no longer serve a purpose that I can rationalize. And all capped currencies should have a "sweep" so that currency is never lost but instead is converted to some other currency.
An example of the first is the cap on Umbari Tami. This was a reasonable cap when we were still under the Corsairs of Umbar/Legacy of Morgoth Level 150 cap. At this time while a few practical uses for Umbari Tami remain, they are mostly used now for cosmetics. This is an example of a currency cap which ought to be removed.
An example of the second is Embers, Motes, and Figments. As I wrote in the first paragraph, there are reasonable reasons to maintain a cap on Embers. And Motes are similar in use for characters under the level cap so a currency cap for Motes is also rational. However, Figments have no impact whatsoever on character power or any other practical function, they are purely for cosmetic purchases and therefore ought to not have a currency cap applied. It is already possible to convert Embers or Motes to Figments on a 1:1 basis in quantities of 1,000 units per action. I have suggested in the past in
https://forums.lotro.com/index.php?forums/player-suggestions.30/ that excess Embers ought to sweep to Motes, and excess Motes ought to sweep to Figments, and there ought to be no cap on Figments. Excess Ancient Script could sweep to Figments on a 1:1 basis as well.