I'm going to guess this has been posted already, but...
Notification if the receiver already has a gem store item
I understand it might not be as useful with something like infinite tools, but for skins (outfits / weapons / backpacks / gliders, etc.) it would be nice to know if the intended receiver has already unlocked the skin.
I'd like to gift people some skins (the earmuffs with wintersday for example, or an outfit for a friends birthday), but the fact that I'm not sure they already have it unlocked (and then just basically waste my gems on nothing), prevents me from doing so.