The scripts that can load new objectives into current mission are already here
http://forum.1cpublishing.eu/showthread.php?t=21518
They are used in a mission on Syndicate server right now.
We just need more mission-makers to create more online missions to link them into more or less long campaign.
I do not think devs will do it. They will hopefully just provide an SDK with more tools and better documentation one day. All online wars in original IL-2 were created by community.