Is it planned to use SPIP as a basis CMS for CIVICRM?
From what I can see, it seems that SPIP is a CMS and not a CRM.  While there are no plans for native integration between CiviCRM and other CMSes beyond the four currently supported, many organizations still integrate CiviCRM with their existing CMS.  Simple integration options include remote profile submissions using snippets.  You can also use remoteform, which also works with contribution pages.  

If you wanted a deeper integration, you could use CiviMRF, but that would take development work.