Thanks for your post, Malcom. Certainly the FIA-FIM need not be involved. An "international land speed racing authority" needs only an agreed "template" for vehicles and racers to adhere to, with scrutiny before and after a run, much like the FIA/FIM duties at the Shootout, but possibly like the busy tech line and/or impound on the salt. I'll note (that) the Speed Record Club in the UK has an international membership with interest in air, land, water speed record factions. Certainly there is a lot of overlap in NA regarding interest across speed records venues.
As to the "why do this," I'll argue that it becomes somewhat of a world competition, a la the Olympics. Top speed in a class is a gold medal. Who's the gold medal holder for the world? . . . . It's hard to beat Bonneville as an event. But as the economy shifts, the cost and difficulty of travel increases, inflation with effective loss of purchasing power, well, it appears a world wide activity, that's happening anyway, would allow kilo/mile/1.5 mile participants to play at the big casino table with racers on the other side of the world.