RVSM
RVSM is still a crap shoot for the 20's. Until it is approved I wouldn't count on it. There are a lot of operators who are counting on it getting approved. And even if it is approved, it will depend on how much it costs. If it is too high we'll see very few 20's flying in the future. The quotes out there right now are $150K to $175K. But remember they original quotes for the G2 were running $250K to $300K. Some have been as much as $750K. In my opinion, if the RVSM stc goes much above $250K to $300K we will not see too many 20's flying.
There are way to many issues to handle. The autopilot, 2nd Flight Data Computuer, Pitot/Static system, altimitry, etc.
As for hush kits, there is a kit out there by Bizjet. Seems to work, but you lose the T/Rs. They have not sold too many of them.