This issue has been closed as 'Won't Fix' due to an extended period of time without updates. If this issue is important to you please let us know by posting on the AnswerHub or UDN, and Epic will re-open the ticket for further review.
Blueprint viewport doesn't show the camera preview.
1. Create a new project
2. Create a new blueprint
3. Add a mesh or sprite to the blueprint
4. Add a camera to the blueprint
5. Make sure the blueprint viewport tab is set to perspective
6. Select the camera
7. Take note if a small preview window appears.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-8930 in the post.