Sami has said no to placing arriving aircraft on the market for technical reasons: http://www.airwaysim.com/forum/index.php/topic,37210.0.html
I agree with the rest though, all would be good to have.
Well, the trigger could be set to take place after the aircraft is delivered. If a functionality is created to get all of the above done, sending aircraft to used market would just follow the same functionality.
The programming actions would have fields:
- Aircraft ID (tricky one but could be resolved to something that exists for current and future aircraft. Limiting it to aircraft about to be delivered, which exists on scheduling page) would be sufficient
- Time (well, the question is if it is to be triggered before other actions - aircraft deliveries, terminations or after
- Action parameters, if any (useful for sending aircraft to use market)