Now that I've read most of the Simonson run, I have a few more potential roles for Alice Krige:
Angerboda--this is Hela's mother in myth and on the Marvel Wiki (Loki being Hela's father, as Elizah has pointed out). In #360, Thor uses his father's runes to summon her from the dead to ask her the way to Hel. Krige has said her role would be small, and this is a small role. (http://marvel.wikia.com/Angerboda_%28Earth-616%29
Wyrd--one of the Norn sisters. The Norn sisters control everyone's fate by cutting off each person's thread in the tapestry at the appointed moment in time. We primarily see them in #348, though there is a small coda in #374. Simonson appears to be the only writer who calls this sister "Wyrd". On the Marvel Wikia, she is called "Urd". (Wikipedia says these two names are cognates, and further, the old English word "wyrd" became the modern English word "weird".) This is also a small role and could potentially be unrecognizable. http://marvel.wikia.com/Norns_%28Fat...28Earth-616%29
Personally, I would really love to have an element of fate included in this film. The Vikings believed more strongly than we do in a fixed fate or destiny. That comes through in Simonson's writing, and I think it would be an engaging addition to this film, too.