You can import not only completed games, but even templates that can be more or less at a finished state or just a little example.
The Asset Store has both.
Here for example you can see a template I made for an horizontal shooter in 8-bit style:
You can try it in the Arcade:
Here instead I have created a template for a First Person Shooter on Rails:
You can try this too:
You can also have a look at bundles, for example, I have joined here other creators in order to offer at a discounted price many different types of templates for games: