Perhaps instead of the showcase running off of the hoard itself, perhaps it could be its own stand-alone public 'storage' of sorts.

As it stands, the showcase only counts and shows what you have in your hoard or in your buried tabs - so if you end up selling items from the hoard, they disappear from the showcase...and if you want to show off numbers, putting all those feathers and skulls in the 'buried' tab starts getting pretty cluttered.

What I'm suggesting is perhaps to allow users to 'drop in' the items they wish to put into their showcase. It would act much like the 'buried' option, the only difference would be that it's on display.
This way, there's no clutter and no accidental sellings of anything.

The showcase would still function and display as is.
You'd just be dumping the items you want into it instead.