Wouldn't it be in GitLab's best interest, being the newcomer, to integrate way better and enable a smooth transition?
Maybe we could open some issues and talk about what you'd like to have but is missing, or some things you think we're doing wrong.
* You could use our API to integrate with GitLab [1]
* You could develop a fullblown project service and contribute it to the codebase [2]
* You could use custom webhooks to add custom functionality [3]
[1] - https://docs.gitlab.com/ee/api/
[2] - https://docs.gitlab.com/ce/user/project/integrations/project...
[3] - https://docs.gitlab.com/ce/user/project/integrations/webhook...