Originally Posted by Han Solo
I can see Hemsworth pulling off an epic Aquaman. But he's still Thor, I think it'd just feel weird.
Best reason to let his brother take it. Have him bulk up just like his brother did for Thor. I would also hire the costume designer for MOS, as that new Supes costume made in a dark green leggings and golden or bronze (NO ORANGE!) that compliments his musculature and there you go!
Liam is up and coming and is good for a full trilogy (plus JLA) so he will grow with the role.