Part 4 is now in beta and you can complete the campaign! Some of the highlights include battles against Benevictus' Battle Angels and the "Citadel"-area where most of the action takes place.

How to access beta: https://steamcommunity.com/app/2065810/discussions/0/3720566578371791473/

However, this is not all - as we're beta testing Part 4, we're also working on NG+ which allows replay in higher difficulty levels. But for now: Grab the beta and send us feedback and we'll fix any major issues before moving the Part 4 into the default branch. Couple of Part 4 images below.