Let's imagine this, to solve all the IF and ELSE about riders, skills, bikes and tires.
One event a year, whose bike and tire sponsors are drafted among the one taking part to the MotoGP championship (and willing to participate, of course).
So, one bike, for everyone, which is allowed to be customized only for ergonomics.
The bike sponsor will have to provide bikes for the racers. It's $$$, but the marketing potential is high, and collectors would likely kill themselves to eventually own the bike used in the trophy by their favorite rider.
Few sets of different tires, among which the riders can chose depending of race conditions. One sponsor, or maybe many, since the riders will be free to chose the best tire for him.
One selected track where the event take place.
Race on Sunday, but the event starts the weekend before, with large media coverage and riders participating to the opening, and interacting with fans.
Sponsors have the chance to use that as advertising event for new bikes and gear, among the fans taking part to the opening.
A few wild cards might be given to riders of other categories, as long as they will qualify in terms of time on laps.
Monday to Thursday for the riders to test the bikes, and adjust the ergonomics. No engine changes whatsoever allowed.
Media coverage of the tests, with interviews with the riders all along the way.
Friday and Saturday it's laps timing for grid selection, and Sunday The Race.
Sunday night party with strippers and booze!