The difference?
In RPs,the idea is used by all in the RP.
In fan fictions,the idea is only written on by a person.
In fact,if there are fan fiction based on RPs and RPs based on fan fiction,I say go for it(provided the original user is fine with it).
And since no one has yet to start a pitch,I'll get the ball rolling.
It's the year 2257. The FX-500 is now a nostalgia league raced by members of the old guard who prefer more conventional tracks and controls. The R-1000(or whatever league you want it to be,it can be changed and revised if needed),however,is the current Anti-Gravity League. There have been many changes to the racng scheme,as,now,pure speed does not guarantee victory. Among the new race types is the Artistic Race,where spins,rolls and stunts are the things that decide the victorious. Another Race Type not in the Leagues of the old guards is the Zone Race,where zone increases ala Zone mode. Unlike Zone Battle,there are no boosts or shields,and points and finishing position are factors in deciding the factor.
A difference between the current leagues and the leagues of the past is that the current leagues can tap into existing tracks for use in the race calendar,so the race world does not suffer any "drought".
Companies,both government and private,are either the teams themselves,or are contributors and aiders to a team. Hence,there are many "cliques" where one ship is used to carry the "banners" of more than one company.
(If anyone has new ideas,or would like to add to this,reply)