I don't get if multi repo approach is flexible, why we should let it go. I only see single repository that may be simpler for one person : the release manager. But well, we can improve the release tools !
If there are less dependencies, we do less tags/releases and then release are also quicker to do.
If there are more regression tests, the need to do bugfix version is decreased :)
And I live in the same world so I don't see what Eclipse Che environment would be different of any existing major project ? Why Eclipse Che would be an unique case ?
Developer of a plugin don't care about the release process of Eclipse Che. He only needs a version of the product to set in its pom.xml and launch maven that do the job.
And derivative work of Eclipse Che will have the same problems of 'multiple repositories'. (as it will not be included in this 'one single repository')
So taking directly the 'multiple repositories' approach will match all derivative work of Eclipse Che and then all people can centralize and use the same tools for assembly.
Then it will improve quality.