Originally Posted by
LeisureFirst
You can't have an aircraft containing a mixture of cleared and uncleared baggage, so your suggestion would rule out customs preclearance.
Even immigration preclearance for just some pax is a bit dicey, because instead of the passengers just strolling off the plane like then do on BA 1/3. their passports would still need to be carefully checked to make sure they'd be pre-cleared and also were the same person - yet more queues.
OT, but in India, exactly this happens - international passengers on AI flights clear at their final destination, and on domestic legs on international flights, domestic pax are allowed onboard the flight. So at the destination, bags and people are segregated based on bp/e-ticket number, and only some have to go through immigration/customs.
It's not a fun system to deal with, but flying on 777s domestic makes it completely worth it...