https://www.kickstarter.com/projects/rain-world/project-rain-world/posts/1925219

Free expansion is being developed that will add an easy (and a hard) mode and more creatures, amongst other things.

Free expansion released! The additions are:

- Two new playable characters that function as an easy mode and a hard mode.

- Local multiplayer, with an arena mode and a sandbox/level creator where you set-up custom scenarios based on what you've played to play through together.

- More creatures, items and secrets.

Co-op for the campaign still to come in v2.0.

Developers have been hinting at what appears to be another update, to be released in a month or so.

gues we get a switch version but not a 2.0 . not that im complaining....except i am cause i'm a big whinnie baby and i want more. like campaign coop

They're bringing out update 1.7 at the same, which might include co-op. No-one knows for sure what will be in it, though.