1. /usr inside /: we have been through that recently enough in debian-devel. There were many objections, and it was rejected for the time being.
It is very unlikely to fly until RO / becomes a reality. And unlike /run,
since it has been recently rejected, any attempts to get this deployed without getting most of the issues addressed are likely to backfire very nastly.
And you cannot have "no /usr" if you don't solve this one first, as all reasons for rejecting it are also valid for "no /usr".
2. no /usr: an EXTREMELY HARD sell. It causes a major mess on / and to my knowledge it will give us no strong technical advantages at all. It needs to wait for (1) above to be resolved, anyway.