I have spoken to controllers who reckon they can easily handle the small number of aircraft that havn't yet been able to get a manufactures service bulletin for the upgrade.- just as they did with non RVSM compliant aircraft.
If I was a professional controller I would not like to be told that I had to force business jets to low levels( up to $1000 per hour extra fuel cost as well as the WX worries) unless there was a good reason for it.
I would want to provide a professional service to all that were paying my salary- not force their passengers into operations with lower levels of safety.