If they had a solid sync service between GitLab and GitHub; PRs, issues, code, everything then things could get interesting and some people might consider the switch.
You can also sync any remote repository (two-ways) [1] in GitLab EE (which runs on GitLab.com).
I made an issue for a continuous sync in GitLab [2]. Would love to get your feedback.
[0]: http://docs.gitlab.com/ee/workflow/importing/import_projects... your project from GitHub to GitLab
[1]: http://docs.gitlab.com/ee/workflow/repository_mirroring.html
[2]: https://gitlab.com/gitlab-org/gitlab-ee/issues/904
If they had a solid sync service between GitLab and GitHub; PRs, issues, code, everything then things could get interesting and some people might consider the switch.