Meyer said take it to Experimental to advance it. In particular, how SSM can simplify things if the source is well-known. Shortest path tree can be created right away, doesn't need shared tree and data to renegotiate path. This turned out to be controversial. There are knobs to do specific SSM things, but wont hard code anything.
Some mechanism needs to be implemented, filtering or hard coded.
Content providers wanted more addresses. So don't filter till most hosts and routers are using IGMP3. Its not enough for iana to say don't do it. Filtering in the application layer goes away if they upgrade. But, address collisions can occur.