I was looking for a way to inject custom page into pipeline UI (to display reports, i.e. HTML Publisher Plugin support for Blue Ocean UI), but as it turned out, there are no extension points for that. So this is a feature request for

• extension point for links in top bar (to add custom link like Changes, Artifacts, even if it leads outside of current Jenkins instance - it could be staging environment or something like that)
• extension point for new tabs
• extension point for adding custom elements like additional links in artifact display cell (so actions like download this artifact, but custom ones, for example store this artifact in S3 forever, would be possible to implement)