https://pr.dim.gg/10584/ has a version of this. It's a bit weird, since some items don't show as collected for some reason...

@philkernick did you have a chance to try this out?

I can see it's been implemented as is:collected. Which means to find the uncollected, I need -is:collected. The screenshots below have -is:collected applied.

Mostly it seems to work as expected, but I note the following minor issues.

For the craftable exotic mission catalysts they still show up as uncollected, but if I click into any of them they say unlocked in collections.

Emotes and ghost projects are not consistent. All of the ones that are not shaded should not be shown as I have them.

Universal ornaments are also not consistent.

The blue ticked ones are unlocked in collections, so shouldn't be showing here.

Yeah, this is only implementing the same check that vendors uses, in the spirit of "I'm proposing this exact functionality be exposed as a filter is:uncollected". It doesn't have any extra logic to handle all the other special cases in collections.

Since there hasn't been any other interest, and the definition of "collected" is so difficult, it's not worth it.