What I would love to see in 1.5, in no particular order.
Cooking Skill and Minigame
It would be cool if Cooking was an actual skill and I'd enjoy it a great deal more if there was a minigame involved. The miningame could determined the quality of the dish (basic, silver star, gold star, iridiuim star).
Bug Collecting
Give us a net and let us collect bugs (which could be displayed in the museum). Fireflies could be out during summer nights, grasshoppers could be in tall grass, dragon flies near water, bees near flowers, beetles could be in trees, etc.
New Area to Explore
I'd love to explore a bayou with new plants, forageables, and freshwater fish. But really, I'd be happy with any new map to explore.
Tropical Farm
A beach farm would be amazing. It could have a significantly reduced farming area, but could offer beach forageables, saltwater fishing, and allow us to grow palm trees.
Stardew Valley Tribune subscriptions
I hate having to run to Pierre's every day to check for quests. I'd happily pay to subscribe to the Stardew Valley Tribune if it listed daily quests in a Help Wanted section. It could also review festivals, report on things like meteor strikes or UFO sightings, and feature interviews with Pelican Town citizens in which they flesh out a bit of their backstory and give hints about their liked/loved gifts.