Please hear me out, I aim to suggest what I imagine would be a lo-fi way to handle excess luck in the game for capped players (who are already a significant minority).
So we've heard before suggestions about a luck eater/converter in the same vein as Mawdrey II, Princess, etc. Those are nice and all but to me they fuel a different problem in that if they are converted to bags to open then 1) they will indirectly generate more luck (albeit a low feedback loop), 2) they will directly generate more materials/raw gold, 3) adds yet another slow sink to something that can accrue quickly depending on your in game activities, and 4) isn't really the point of luck.
If I remember correctly, part of the effort to make blues/greens more valuable and worth to salvage was adding luck to the game as a way to increase personal magic find account-wide. Once hitting the cap, the only motivation to salvage blue/green items is for their materials and luck is only a sort of clog for the hoarders (myself included).
What I propose is adding a single Mystic Forge recipe for the Exotic tier of Essence of Luck that accepts 4 stacks of 250 essences (aka 200,000 luck total) and returns a single booster. Now whether this booster is a brand new 5% Magic Find booster that stacks with others, or is simply an Enchanted Reward booster or pure RNG booster, that's up to implementation. There are now X problems with this.
As for the 1, either with the implementation or a later date I'd hope that extra luck that had been consumed could be 'spent' at a vendor or mailed to the player (like karma jugs with the change to boosters' interaction with consumable karma change). Number 2 could be addressed with a vendor as well for a conversion ratio of 2 Legendary tier luck for 10 Exotic tier luck. Number 3 is the doozey, and the only way that I can come up with to mitigate it would be to just use a booster that stacks, or some other existing booster that doesn't compete with the boosts given by the candy corn one. (Or even adjusting faucets on candy corn during H'ween & from Trick-or-Treat bags to account for the delta in consumption, but I'm not an economist.)
So basically the idea is simply a Mystic Forge recipe to start for a booster either RNG or Enchantend Reward to start so that it takes only minimum development time/effort (hopefully!)
P.S. As a current web developer, I understand that back end systems aren't all that they appear to be - so if even this would be a high effort change, I definitely understand if it were denied.