I think It's simple: most likely current character customization is hardcoded to only accept/show a certain amount of options for each category. When they say it's difficult they probably mean the whole thing needs to be revamped.
Honestly, the only thing I can think is that maybe that Midlander isn't just a "face-option", but is literally a custom model, that cannot be changed AT ALL?
Which, even if that were the case, personally I would still love to have the option to play him.