I think it would be really great if we had some more mailbox quests to do. I've always wondered why there isn't a quest where the Dwarf sends you a letter in the mail asking for some milk to try. "One day you'll have to tell me about this beverage you call milk." Maybe the quest could proc shortly after you speak to them for the first time after acquiring the translation guide? What kind of mailbox quests would you like to see if more got added in the future?
Mailbox quests might be a venue for putting a little more emphasis on fruit trees. Currently, only Emily asks for an apricot in Spring of Year 2, though the Community Bundles do encourage an Apple and Pomegranate tree.