We have some low-level stuff on our roadmap (e.g. federated Merge Requests [1], federated GitLab instances [2], cross-platform mentions [3] - i.e. mentioning GitHub users). These didn't get prioritized yet, but it's only a matter of time. We have limited resources so we have to prioritize and scope out releases in a such a way that it advances both our vision and satisfies customer requests.
A really interesting low-level component that we created and use in production is gitaly [4] (which is a git RPC component that aims to completely remove GitLab's dependency on NFS for repository access - and replace it with gitaly itself).