Generally you need crew training. That's why you saw AF doing CDG-LHR and KE doing NRT/HKG-ICN when they first got their A380s. CZ is doing domestic (including HKG) service for a while with theirs (although it may be part of their long-term plan, too). There's also the matter of the interior being distinct to BA, so you won't know if there are any oddities with how it fits the A380 until you have real passengers using it.