Think of it this way, if Malekith is responsible for killing
IF that spoiler is true, then either Loki or Thor WILL be the one to take revenge on and kill Malekith not Kurse. And Loki being who he is, is more likely to take revenge than the hero Thor will be. Plus the fight is going to be really really cool and different from what we've already seen. They need to change that up to keep it interesting. The death of that character goes far FAR deeper and impacts those characters MUCH more than any manipulations that have been done to Algrim/Kurse. They wouldn't necessarily be ignoring that relationship and the manipulations of Malekith, it would just be the end result that is different. Kurse's revenge on Malekith would be then turning good and leading the dark elves into a peaceful age (sort of like Alfyse does, it sounds like), if this hypothesis pans out.
and it wouldnt necessarily mean total redemption for Loki, it is only a gesture that he still cares for his family, and could be seen as a bit of an olive branch I suppose to Thor. It is still revenge though, and that is not usually seen as redemptive. When Lucas first titled Return of the Jedi, it was Revenge of the Jedi, but then it was changed because Jedi are basically a force of good and do not take revenge. It was however, Revenge of the Sith.
The stuff with Surtur or something similar could still happen in Thor 3.
And I wont hold you to the eatin' dirt and taping it thing.
Edit: Note I've reposted this in the Kurse thread in order to try to keep the conversations in the relevant threads.