There is a deft understanding needed of the magical mythology of Eternia, which needs to convince an audience. Keldor and Randor have a potential camaraderie that then leads to betrayal, thanks in part to Keldor's Gar blood. Hordak must be a pervading force and the kidnapping of Adora (though She Ra needn't be in a first MOTU movie other than as a baby) is essential.
Adam becoming He-Man could be a complete character change. Maybe Duncan drags the spoiled Adam to Grayskull to be anointed with the power sword.
Add in the army of evil and heroic characters and the potential for a "Nolan Dark Knight" trilogy culminating in an interdimensional conflict between Etherian and Eternian forces.
Is Wenk, a hack Hollywood writer, more used to writing quips for action stars with minimal characters and sequences, going to be able to deliver the epic film we want? No. I doubt he will.
Only a person who loves MOTU, like Lucas loved the old scifi serials or Peter Jackson loved the Tolkein books, can deliver a script that will honour the legacy of the franchise.
Wenk just won't deliver a worthy film, worthy of the name. It will be disposable dross - but maybe this disposable, money-making exercise is put through the movie production machine and it is all we deserve as a fandom increasingly bowing to corporate powers and not allowing our souls a voice about this phenomenon we love.