I think the eternals movie isn't going to have too much to do with Kirby, or Grunewald for that matter. I hope I'm wrong but I see little tie-in with Thor. probably Wakanda yes, but Thor no.
Yeah that boat has sailed for the movie and I think if a second one were to feature Thor it would have to re-cast the part. Hemsworth will be to old and/or expensive. A shame since I think both Eternals and New Gods movie are missing a golden opportunity. The idea of a ragnarok leading to a new Thor would just be to cumbersome to add in an Eternals but would have to be in another solo. A possible Disney plus show maybe.