I don't think they planned it with a sequel in mind. It would certainly be interesting but tough to do at least a direct continuation of the story.
I suppose it could be a different type of movie where we follow some other kind of Viking adventure with
Freya and Kainan
. But if you are going for the same feel maybe alien monster inspiring earth mythology you could take any number of routes.
Or it could be a story about Kainan's people and their space conquests. There's a lot of possibilities but probably the hardest one to get right would be a direct continuation from where the movie left off.