A situation they've never faced before?
Like what? Being happy? Not arguing? No angst? That would be new for them.
Or there could be the kiss everybody seems to be waiting for, though there seems to be a lot of differing opinions if it should involve Castiel and Dean or Sam and Dean or all three at once, wonder how that would work out, maybe one of them could be hanging from the ceiling like Spiderman? No? Ok... but yeah they never faced that either.
But with this show happyness and love might be out of the picture. So probably a new kind of misery. I like the black eyed one. King of Hell Dean, human Sam, Angel Cas.
Fire, Earth and Sky. But wait! Where's the water? Oh right, it's probably raining in Vancouver.
I also like the idea of Dean being cured by Sam and maybe they both die in the process. We could have a few episodes in heaven or at least behind the veil as heaven seems to be closed, that would make for some interesting stuff.