My wish is for limited items that appear inside of containers to show as illusionary when not in, or to have some other indicator that a limited item was there when checked (acknowledging coding difficulty).

The reason for the request is the exact same rationale as was used when illusionary items were added to mobs. Previous to that, a player would have no way of knowing where an item was from even if they explored the area fully.

From a coding perspective, I recognize that this is more challenging since mobs check the availability of the item at repop (the item may show as illusionary now, but the item could be available. Kill the mob and it might repop with the item), while containers are never destroyed. Current illusion tag code probably was never intended for container use, current code the populates items into containers would obviously be touched, some containers are permanent while others are items themselves, etc. But I think it's the best ideal solution from a UX perspective.

Barring that, adding SOME indication that a limited item usually populates in a container would be preferable to the nothing that exists now. Something like an echo when you look in the container, "You get the sense something is missing from this container." Just letting the player know that sometimes there is something here and they should check back. Perhaps have this only work for permanent containers, so those rare cases where a mobile container potentially has a limited item inside will still be myserious.

Umi and I are both a no on this one.

For me - this provides no difficulty in the way that illusory weapons and all do to balance it out. And there are some items that quite purposefully do not spawn every time, even when they could. So I'm just generally against it.

For Umi it is the coding difficulty + abusable bugs due to it (opening a ton of issues) for no real appeal.