Originally Posted by The Overlord
Crossbones is kinda like Harley Quinn, he is interesting because he plays off another villain well, rather then just being compelling on his own. Crossbones works because he is Red Skull's number 1 psychopathic supporter, without Red Skull he is less interesting, Crossbones insane version of hero worship is what informs the character. I think the problem is it would be hard to recreate the relationship they have in the comics, Crossbones seemed to worship the Red Skull is "the baddest bad guy around" and movie Red Skull just is not as fearsome as comic book Red Skull, so its harder to see why Crossbones would see Red Skull as an idol.
There's also the fact that their names fit together perfectly as well --- Red SKULL and CROSSBONES. Despite what some folks have said in this thread, you really can't have Crossbones without Skully --- it's Abbott without Costello.
As for the casting rumors about Coster-Waldau and Holloway --- pretty safe bet that Coster-Waldau is vying for someone like Zemo. A lot of people immediately seized on the Crossbones bandwagon when Holloway's name was mentioned; but to me, he makes a LOT more sense as John Walker.