"In the blog entry Mr Stross uses the two experiments to make NON-DNA/RNA based life (if successful obviously) as "phase-changes" of evolution. Which is it? Does macroevolution predict and require that all life will/must use DNA/RNA or doesn't it?"

This doesn't seem that hard to reconcile. Macroevolution predicts apparently that all naturally evolved life will use/must use DNA/RNA [1]. The word "experiment" means to me some action that is made by an advanced tool wielding scientific intelligent being to test a hypothesis. This is not "natural", rather "artificial". And... macroevolution does not predict that such scientific beings will inevitably arise, that's going to depend on the history of a species and it's predecessors, i.e., conditions, environment, blind luck etc.

As for the blog entry, I think it is true that once the conditions where a species can understand and control it's own evolutionary heritage, then Darwinian evolution will be superseded by something more Lamarckian in character. The question is, is it possible for a species to understand and control it's own evolutionary heritage to the required degree necessary to avoid a Darwinian process.

OBSF: Dear Abbey, by Terry Bisson

Stephen Shevlin

[1] Or some other set of complex chemicals that do the same job. Note I have absolutely no idea whether this hypothetical alternative set of complex chemicals exists.