I hope that if the downloadable tracks are not available for online, it's only a matter of time before we get a patch for this.
With an update, i don't get how this wouldn't work.
Races, or tournament games would appear red in the list when the user doesn't own the required pack. And if the user is already in a lobby when a downloaded track is added, then he gets a message and gets kicked / unless it's impossible to add new tracks when some users in the lobby don't have it. Users with no packs would appear red in the lobby / Or maybe a flashing red light asking the users to buy if they want to enter a game… Welcome, fellow pilot ! Only 5€ ! Cheap ! Amazing ! Come play with a billion other racers ! Plenty of 8 players games inside !
A little more complicated, but hey, if we charge for it, it has to work, right ?