I figure Alduin's 'death' is questionable at this point. On one hand, we didn't absorb his soul, but, on the other hand, we defeated him in Sovngarde so he may have already been in 'soul form' and we couldn't get it there.
The enemy scaling should be handled something like this:
Scale them absolutely on Novice-Adept - like the game is currently coded.
Limited scaling on Expert and Master. They could do this in such a way that on Master you would have to have a follower who's leveled and well-equipped to defeat bosses or at least Alduin. They could also 'lock' certain zones by setting enemies' minimum levels to be too high for us to go there at lower levels. I'm not a fan of invisible blocking objects; I realize they have to limit the map at the edges, but that could be handled by large boulders that haven't been 'dug through' for centuries.

Personally, I like to be overpowered at higher levels because I earn it via Smithing, Enchanting, et al (on my first character at least - on subsequent one sometimes I just want to be a tourist.

). That being said, with
five difficulty levels I would think Bethesda could tweak the AI and scaling a bit differently than the standard
character is weaker and enemies are stronger at higher difficulty levels.

Edited for usage.