Hello Steven!
Thank you for bringing this up! There is some in-depth work coming up for pickers in a future release and I will create an internal ticket so that we can take a look at this during that initiative!
For now, I think it might be a good idea to look at the AssetEditorSubsystem as it contains utilities that may be able to help if you want to create a separate tool; but currently, only the filters will really be able to affect the picker/dropdown itself.
Cheers!
Jayden