We have syntax highlighting within diffs since 8.4 https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/2109 so please consider upgrading.
I don't understand what you mean with instantaneous merges, did merges seem faster in the past? We do have a feature that allows you to merge when the build is successful, saving many people lot of time http://doc.gitlab.com/ce/workflow/merge_when_build_succeeds....