It would be nice if we could show when an editor was last active on /user/USERNAME/subscriptions/editor.

The main reason to subscribe to editors is to watch their edits (because they're good, because they edit things you're interested in or because they're bad), but editors come and go, so you can easily end up subscribed to loads of people who haven't been seen for years. Showing when people were last active would make it much easier to remove old unnecessary subscriptions.