In case you were wondering what was actually new in Ghost 4.0, Matt Birchler made a great video going over the major changes.
Weirdly a lot of this was already "available". Albeit marked as being experimental. For example, I've been using the members feature and email newsletter feature for a few months, and I have an accent colour selected already.
The thing I'd like them to focus on next would be for a better mobile/tablet interface. I don't think we'll ever see a native app from them, seeing as they are a web company. But I'd settle for a website that's at least usable on an iPad.