The TC on 5 Sept 2013, in response to public comment #10, passed a motion that stated: "The TC considers this stylistic,i.e. that RFC keywords (bound to OASIS legal statements) clearly indicate what is normative in addition to the normative TOSCA XML schema. The TC resolves to further consider conformance clauses in v1.1, but considers the current approach adequate for v1.0.".
The latest revision of that public response document (for COS) can be found at: https://www.oasis-open.org/apps/org/workgroup/tosca/download.php/50551/latest/TOSCA Spec v1 COS - TC Responses to Public Review Comments.xlsx
I am taking the liberty of assigning one of the co-editors to this so that we don't lose sight of this consideration during future v1.1 editorial work. The editors may choose (and are encouraged) to consider this further and make recommendations.
NOTE: There are OASIS GUIDELINES on conformance clauses. As of this writing, I do not see that they are mandatory. Here is the link: http://docs.oasis-open.org/templates/TCHandbook/ConformanceGuidelines.html