We'd love to know the details and preferences about this as well....We're planning on making more 2D assets and sprite sheets and this would be helpful to know for seamless usage by the user....
From what I understand, Godot is incredibly flexible with png sprites. As long as you have them in a grid, you can import them into your projects. RPGMaker, on the other hand, is really specific with how sprites need to be formatted, so I don't make sprites for it. I've never used Unity or other similar game engines, so I can't say what it's like to import pngs as sprites with them.
Good to know more details about other game engines apart from Unity....We use Unity for production so it's quite helpful to understand the possibilities and limitations of other game engines.....Also, Importing PNGs both as sprites or as sprite sheets works well in Unity, and it also has slicing features for the sprite sheets along with some good sprite skinning/rigging tools in its sprite editor....