There is no current plan to release a "User Experience Open Assessment."
Open Assessments are just one of several ways to prepare for assessments, and when we released PSU I we focused on providing the most meaningful and helpful learning assets on the PSU I Suggested Reading page. In particular there are many blogs which will help you prepare for the PSU I assessment.
The Suggested Reading page for PSU I does include a recommendation to take the Scrum Open and Product Owner Open. Taking those open assessments will help you not only with understanding the types of questions and how they are phrased and organized, but will also help you with your knowledge of the basics of Scrum – which are covered on the PSU I exam. The remainder of the material on the page, in particular the blog section, will help you prepare for the User Experience specific questions.
We monitor the pass rates for all assessments and questions, and in the case of PSU I the pass rate has remained at or above our target since the release of the PSU I, indicating that the learning material on the suggested reading page will help you prepare to pass the PSU I.
Thank you for your response Rob. I have utilised this sites learning paths when provided as well as their suggested reading for all of the exams I have taken so far, and they have not failed me yet. .-)