According to XXF, Lin Dan is only at 80% of his best so my intuition says Chen Long to win. The wild card award took him by surprise, and there's insufficient time, not to mention motivation, to get up to full speed as clearly shown by the three matches he's played so far, certainly not the Super Dan we know.
Yes, the WC is important, a major event, but still an individual championship more for individual glory, not team championship which is compulsory for CHN to win for national honour, in the words of LYB. As such,may the better player of the day wins. It's the QF, not SF, their next round opponent will not be LCW, so they will fight it out in mutual rivalry. I hope Chen Long has the inner belief he can win the world title and go all out for it.
As for Lin Dan,he has nothing more to prove. As he himself has said, winning golds is no longer the most important thing in his life but his legacy and the promotion of badminton to uplift its status in the world. He has already won everything there is in badminton, attaining fame and fortune and is widely regarded as the Greatest of All Time, what more is there for him to achieve other than a more purposeful,meaningful and fulfilling life.