The possibility to Bookmark an Artwork, even if not owning it, to get notifications if it was sold (to which address), got a bid, a new list price, etc.
Example: You find a piece that you love, but you can't buy it right now. You bookmark it and get a notification if it gets relisted, maybe for lower, and now you can afford it!
It might work great for 1/1's but for multiple eds. can get complicated, perhaps keep track of the eds. as a whole.
Possibly making the same way notifications work when you receive an offer in a multiple edition work that you hold, but now, you can get notifications even if not owning the work.
My suggestion is to make this an Optional feature, that can be turned On and Off easily by the user, so no one gets unintentionally flooded with notifications.
And simultaneously enabling the ones really interested in keeping track of how a specific piece is going.
Seconded, I believe that any digital marketplace should have a favorite/save/"heart" feature. Coming across a piece that you want to study or purchase or share at a later time is a extremely frequent occurrence that users have to manage now by either using the bookmark feature on their browser or keeping endless other tabs & windows open. I see this first and foremost as a necessary feature for collectors but yes, allowing creators to observe interest and attention directed toward their work is also an excellent benefit. I def feel it is more useful for individual items (even those that are part of collections) but having the option to favorite a collection would also be nice. Whether a user's favorited items are visible to the public should be up to each user. Whether or not creators get notified of their works being favorited should also be an individual choice.