I can't imagine a Vinland Saga anime, seriously! xD Well, I would be happy for a good adaptation, but it's so... Terrifying. What I mean is thinking about a adaptation scares me because two motives: good/bad adaptation and success. I don't want see a successful anime being a bridge for a bad manga. I said it because the "SnK case": The author don't want "betray" the fans. I know, Makoto Yukimura is not like that, but it scares me. (sorry for the bad english xD)
yeah, i get why you're nervous, because it's such a shame when adaptions don't live up to the original, especially when the manga is such a gem. i don't know much about the snk author or how far they have planned their story, but when it comes to VS, it seems like yukimura has a plan. hell, we know that thorfinn's going to vinland sooner or later, and i doubt that he would let his fans decide the destiny of the characters, or else askeladd and bjorn would still be alive, while canute and thorkell would join thorfinn and company's adventure to the byzantine empire.
speaking of which, i can't wait to see the portrayal of the empire and the culture shock that will happen!