Instead of Red Skull, it should've been Adam Warlock
If this was discussed already, my bad.
Comicbook fans know who Adam Warlock is. He is tied to the Soul Gem and had a big role in the Infinity Gauntlet saga. Those with keen eyes noticed his cocoon made cameo appearances in Thor: The Dark World and Guardians of the Galaxy 2.
I wish the Russo's just had him appear in Infinity War and Endgame as the keeper of the Soul Stone as a nod to his role in the comics. As nostalgic as it was seeing Red Skull again, Warlock would've made more sense, especially since he was foreshadowed in two movies. Casual fans may have been a little confused, but I'm sure their nerd friends would've filled them in, and wiki searches for the character would've exploded for the next few days.