I feel like the number 3 is a pretty special magical number, and in this it is past, present, and future that the fates represent. I think there are other mythos that have this as well but I'm old and drawing a blank (Greek or Roman mythology has 3 fates doesnt it?) . ALSO, and I know you will roll your eyes but whatever!... those stone pillars in Bourne woods, I've looked at REALLY closely. There is the gold sort of twisted crown at the top and the large symbol near the bottom that are extremely similar to Karnilla's various headdresses, and near the top there is 1 sort of flowery symbol, and below that 3 more smaller ones. THIS is why i feel so certain that Bourne woods is the outskirts of Nornheim. The one flower at the top Karnilla and the 3 below representing the 3 Norns. Whether we see them or not in Thor 2 or ever, I dont know but I feel confident that those symbols are meant to represent those characters. I feel like if we get Norns at all, it will be 3. However, it may be something that is simply an "Easter egg" nod to those characters, but we wont actually see them in the MCU.
Also, Sam mentioned before a old woman that was prophesizing Ragnarok, Volla, I think, and I know Karnilla has Haag by her side, so maybe something could be done with that for a character, possibly instead of using the 3 Norns in the story.
Okay, in regards to changing Kurse, what do you think of instead of Malekith sending Algrim down in the pit with Thor, he steals and uses the Tablet of Life on him? I see it has been used in Spiderman in the comics, but it IS an item in Odin's vault. And in the description it says...
Kurse could still blame Malekith for turning him into a monster and turn on him later, I suppose. I dont really see anything in the vault, other than the Tesseract that might do that, or the IG, but then it sounds like the 9 realms are in some pretty deep doo-doo if anyone else gets a hold of that.
http://marvel-movies.wikia.com/wiki/Odin's_Trophy_Room