I've been watching several people (FuryForged, KatherineOfSky, Zebra Gamer) play Forager for the last few weeks. This game is amazing, so I must give kudos where kudos are due! I do have a few suggestions, just off the top of my head.
Shovel Upgrades - These would allow higher chances of digging up rare objects and jewels
Story Mode might be a cool thing to add, as there are tons of Quest Givers available on the map. Maybe finishing all the QGs main quests unlocks a quest to take on a Big Bad, say... a Dragon?
Adding Plums, Apples and Peaches, as well as Plum, Apple, Peach, and Pumpkin Pies. This will add some variety to the tree drops and could even allow for specific fruit to drop in different biomes.
Building Upgrades - By Upgrading a building, it not only works faster, but even has additional slots to do work in (forge, vault) or more items for purchase (market)
Allowing access to special buildings, like the Druid's Tree; and access to already finished Dungeons so players can grind materials (Finished Dungeons would yield no Experience)
I hope these are some good suggestions :)