Rather that re-write the entire online matchmaking code, why not just choose a simpler method. Stop selling individual cars. Sell only packs. You still will have those that have only 1 or 2 of the current 3 endurance GT racing packs, but the vast majority will buy what is offered and thus 'most' users will be able to join without worry. Just sell packs, just buy packs. Issue 'mostly' resolved.