WowAce

The one feature I've always been looking for in a “sell junk” addon is the ability to automatically remember every single item I've sold manually and add it to its item sell list. (In reverse, manually buying-back an item from the vendor should automatically remove it from the list again)

This would obviously depend on being able to detect when I manually sell (by right clicking on) an item. If that's easily possible, then this seems like an easy feature to implement.

That said, it does complicate some of the internal design, simply by virtue of the junk list most likely growing very large over time. An amortized O(n log n) or O(1) data structure would be beneficial.

Do you think it's possible to include this in SellJunk, or is it out of scope?

I think that there are no plans to implement this.

The aim is to stay as lightweight as possible.