here. Here is something that would be more difficult. The talents of Anderson or Stirling might be up to writing a sequel to CS Lewis' imaginative works, e.g., to describe a joint meeting between the Friends of Narnia and the Council of Logres. It would be necessary for the author either to share or at least to have an empathetic understanding of Lewis' distinctive brand of Platonic Anglican Christianity.
Lewis imaginatively restated Christianity twice. Christ is both Aslan and Maledil. Lewis wrote his four (one unfinished) Ransom novels as replies to Wells' accounts of space travel, time travel, interplanetary invasion and the future of society on Earth. His narratives are also anti-Stapledonian. Thus, Lewis, like Anderson and Stirling, is an essential part of the dialogue of twentieth century science fiction. His psychological and moral insights particulary in Ransom Volume III, That Hideous Strength, and in the allegory, The Great Divorce, are of immense value - quite apart from his imaginative accounts of other worlds. Unfortunately, Lewis was anti-Darwinian but that is part of the continuing debate.
Anderson and Stirling continue the tradition of Wells. Will anyone continue the tradition of Lewis? (Philip Pullman, who is currently extending his fantasy series, is post- but also anti-Lewis. James Blish was a post-Lewis Wellsian sf writer.)