Currently it would be difficult to say. He's been asleep since 4.4, and he may not wake again during the WoL's lifetime. However, he would not be surprised by the WoL's transition into the WoD, their increased strength through overcoming the trials on the First, and becoming the champion of two realms. What might take Middy by surprise though is that the WoL/WoD is not one, but two souls. And each of them possess a heart of phenomenal strength. His take on that would be interesting indeed.

Over the course of time, Midgarsormr's view of the WoL changes, and through them gains a better understanding of man, their heart, and their resolve. While he does not say this directly, my own personal headcanon is that this knowledge would have very likely saved him during the battle of Silvertear. He clearly underestimated a power mankind possesses but does not exhibit through force. When we first meet him, he is honestly still quite bitter about his defeat at the hands of man. When he finally accepts this through the countless feats of the WoL, his respect is shown by referring to them as "Child of man".