They are displayed in merge requests but not anywhere in the normal CI pipeline UI and I'd live to be able to see those and see what works and what doesn't.
Yes - that's something we want to get to this year. We call it "CI Views" right now but we want to expose better all the types of test results that get collected by GitLab. Today for XML (JUnit) results, you can see what fails in the merge request with https://docs.gitlab.com/ee/ci/junit_test_reports.html.
But we want to make the XML, JSON or HTML output of _any_ type of test first class with CI Views: https://gitlab.com/gitlab-org/gitlab-ce/issues/35379