Maybe you should ask what GitLab users want too 
They should the center of all your discussions.To me it seems evident that GitLab remains the principal place where the development occurs, SonarQube analysis being just a part in the whole dev process.
In the merge request I’d like to get a good summary of what’s the quality of changes going to enter. Did the test coverage increase? How many new issues are added/resolved? etc…
Please note that with the current plugin you can break the pipeline:
That being said I agree that GitLab extensibility points are not perfect for now.