If I were to make my own..... I would probably make it like Minecraft/Rune Factory xD
First off, it would be pretty much the same except you spawn in the middle of a forest with no villagers and just nature. You would have to shake trees until sticks fell out, use those for making tools, and collect resources. Ore rocks would provide stone, and chopped trees give lumber, and with those you can make a piece of table furniture. Furniture would be allowed to be placed outside, making it a more free and open world with tons of new combinations! With enough lumber and stone, you can craft a house, and decide where to place it. Once you got it set, you can go inside like a regular AC house, and start decorating it with furniture you craft! There would of course be two new major sets: stone and wood sets (which would look made out of AC wood and stone).
Later on, you can collect bugs, flowers, mushrooms, fruit, and other items, make those into dye or collectibles, and customize your furniture into the traditional AC furniture sets you see in most games via crafting.
AC is a vegetarian game, so of course the ability to cook fish you catch will be added!!!
you'd of course cook those in a piece of furniture you crafted. Other meats would probably be left out due to sheer horror of butchering villagers lmao
You would also be able to farm more fruits and things, including basic vegetable crops, berry bushes, fruit trees and bamboo, but also sugar cane and other crops too! With those, you can craft them into ingredients on certain kitchen furniture, and make those into food to eat!
A hunger bar would of course be added, so you actually
had to eat, or you'd pass out and drop/lose all of your items and spawn in front of your house like when a scorpion/tarantula attacks you.
Speaking of scorpions/tarantulas, I would make them the main enemies in the game, where you would have to kill them before they killed you. They would spawn at night everyday, and unless you had weapons, you wouldn't be able to kill them easily. (Similar to mobs in minecraft)
Finally, villages and natural stuctures would be present. For villages, they would be clusters of AC villager houses, and inside they'd be decorated and have random AC villagers. You can talk to them and ask them to move into different houses, or stay outside. But if a scorpion/tarantula finds them, they'll kill them!! Or you can kill them yourself. Killing a villager is the only way to recieve that villager's picture. Besides that, you can take stuff from villager houses and redecorate them, etc, as if they were a house you made yourself. There would also be little garden plots outside and stuff too.
Other things like temples would be building with rare sets, like a ruins set, cave set, temple set, etc. Also! You would be able to breed flowers like in AC:NL and use those for the main set of dyes for customizing furniture.
.... I have so many ideas XD