If a solid replacement -- and at this point it looks like Sponge -- creates an API that is usable and stable, we'll switch to that. I don't see Bukkit coming back anytime soon, the community is practically dead. The entire BukkitDev Staff, myself included, has resigned and just sitting in the chats it definitely appears dead. The community has been scared away due to poor management by Mojang, and I fear it may be too late for Microsoft to turn it around.
So in time could ProjectKorra be ported to Sponge? Yes. I absolutely detest Bukkit as of late and can't wait to switch, however, I'll keep personal feelings aside to do what is best for the community. I will wait until we have stable versions of Sponge before we do anything.