We are working on integrating GitLab (enterprise edition) in our tooling, but one thing that is still on our wishlist is to create a merge request in GitLab via a command li
It's not natively supported, but it's not hard to throw together. The gitlab API has support for opening MR: https://github.com/gitlabhq/gitlabhq/blob/master/doc/api/merge_requests.md#create-mr