While I don't think we will see any major update for this game, I still have some ideas:
1. In-game counters for some stuff we for now only get an achievement, especially the pages, but birds and bees too.
2. Ability to return to the island to find missed stuff.
3. More points of interest highlidhted on the map besides current quests. If quest or point is chosen, instead of the hand pointing in the corner, dots similar to those on old maps leading to treasure would appear in the overworld leading to the objective.
4. Fast travel points: could they be either places like Noonibhouse or sky gazing spots or both.
5. A small cutscene of Moomintroll reuniting with his parents. I get that his relationship with Snufkin is a big part of the story, but Mamma and Pappa also were quite involved, especially at the end.
6. A proper post-game instead of reload of the file before Snufkin and Moomin went to open the dam. Aside from visuals in places hit by the drought nothing would change instead maybe aformentioned abillity to return to the island (now during the day) and replay some levels, especially the Groke one for the achievement. Little My in well,missing Cedic and Snorkmaiden side quests could be moved to that post-game.
7. Ability to zoom out the camera in the main area outside of minigames and cutscenes. It would be helpful to get around.
8. Park maker for the players to make and share their own park maps more challenging than the ones in game like in Picross Touch game.