All I know is that they did mention pre-release that there would be no option to upgrade from one edition to another.I never saw a comment whether or not they would add such a system or not, so until I see otherwise I will just expect that they won't add it.
Still a bit odd if you ask me.I can't remember seeing a game where the option to upgrade editions later on wasn't a thing.So before I saw their comment on it I was expecting us to be able to upgrade.Personally I don't really mind, as I'm not interested in the extra Ultramarine skin.But it's sad for others who do and are now forced to pay full price if they want it.