We're also hoping to see them contribute back features to GitLab they need for complex projects, and I think we've already seen a few.
Also, this blog was published when Freedesktop announced their move to GitLab (incl. CI): https://www.fooishbar.org/blog/gitlab-fdo-introduction/
We actually have a panel with representatives from Freedesktop, GNOME, and KDE at GitLab Commit in London (https://about.gitlab.com/events/commit/#schedule)in a few weeks discussing their experience with GitLab.
We're also hoping to see them contribute back features to GitLab they need for complex projects, and I think we've already seen a few.