Pretty sure Dinan mods are still covered by the factory warranty, at least according to their website. Also all the BMW race teams in Grand Am and some of the European classes are running Dinan engines, so clearly there is some sort of tie between BMW and Dinan that doesn't exist with standard tuning companies.
The Shah's Bugatti is on loan to the Frist Center in Tennessee for its special exhibition "Sensuous Steel." It hasn't been sold. Museums often loan each other pieces of art or vehicles for exhibitions.