BTW, did you give a try to "Multiple SCMs Plugin"?
https://wiki.jenkins-ci.org/display/JENKINS/Multiple+SCMs+Plugin

Sorry, did not see that this is in a different component.

Is it really related to scm-sync-configuration plugin (https://wiki.jenkins-ci.org/display/JENKINS/SCM+Sync+configuration+plugin) ? Or more generally to the jenkins core (and SCM) ?

The multiple SCMs plugin is identified as being "proof of concept" code and the author furthermore (and correctly IMHO) suggests this kind of functionality should be in core. Is there a reason this can't remain outstanding as a valid feature request? Other commercial CI servers have this built in, so it doesn't seem outlandish.

I'm asking because currently, the component is scm-sync-configuration (that is to say SCM Sync Configuration plugin)
I'm the maintainer of this plugin and I don't see how this issue is related to it.

If I'm right, you should un-assign the issue then change its component (to "core" for example) in order to have the correct component maintainer being notified.

I suppose you need an abstraction layer like SCM Api Plugin

This duplicates JENKINS-7192, as it was unrelated to SCM Sync.

Wrong solution

How can you close this ticket when the multi-scm plugin clearly states: "This plugin is more of a proof-of-concept than a robust and fully functional component. It does work in my particular build environment, and is meant to serve as a demonstration of what might be possible with more work. It was inspired by JENKINS-7155 requesting multiple repository checkouts for Mercurial similar to what is possible with the Subversion plugin. It's currently implemented as a plugin, but if enough people find it useful, I think the idea would work better in the Jenkins core."? - https://wiki.jenkins-ci.org/display/JENKINS/Multiple+SCMs+Plugin

This needs reopened as it should be a core part of Jenkins.

The multi-scm plugin does NOT work well with CI / GitHub integration.