I couldn't find anything about this by searching for "Haldor Mistlands", so I'm guessing it hasn't been pointed out yet and I'm justified in posting this hypothesis for peer review (correct me if I'm wrong pls):
IMO, and pls correct me if u feel differently, the stone face on the Mistlands building we were shown a few months ago features quite a bit of similarity with Haldor's face – see picture for compairison. Additionally, about a year ago, in this AMA (https://www.reddit.com/r/valheim/comments/nxpaq2/developer_ama_110621_summary/) Grimmcore mentioned that Haldor's brother might be coming to the game. There was also a comment from Grimmcore in a YouTube video (I think by Gaming with Kristi, maybe 6-9 months ago, not sure, sry) indicating that something which is tame from the start will be in mistlands… Could also be the rabbit tho… And lastly I wanna give credit to the YouTuber TerraTanzanite who theorized that there could be another trader in Mistlands in this video (https://www.youtube.com/watch?v=TpTFhmSOlLY). If u think about it… Putting new NPC's or a trader in the Deep North or Ashlands doesn't rly seem fitting, so Mistlands is the only biome left for something like that (aside from having them float on randomly placed raft-platforms on the Ocean xD).