Right now I'd say we need to make it easier to work with nested params so you can easily save Parent + (n) children. Easier handling of uploaded files is another big one. It's being actively worked on right now. There are a few more escape hatches that are needed when you need to break out of the framework. But overall it is fairly full featured.
You can check out our roadmap to 1.0 here: https://docs.google.com/document/d/1EYzx37Kq5h7iLH9SQTFyXNwb...