We'd recommend reading the original piece for the full overview, but effectively Richard Leadbetter argues that PS6 backwards compatibility could see a significant boost if the next-gen console utilises PS5 Pro upgrades as its baseline – as is the case with PS4 Pro and PS5. Nice!
More importantly, Leadbetter notes that Sony's AI-based upscaler, PlayStation Spectral Super Resolution (or PSSR), is in its infancy on PS5 Pro – and is likely to be upgraded for PS6.
He writes: "We are looking at such a big change here that absolutely we should be looking at PS5 Pro as the console that sets the ball rolling for Sony in an area of crucial importance. I'd even venture to suggest that PS6 may even need PS5 Pro to exist for this evolution to happen. Sony's technology groups need time to develop technologies like PSSR and to ship them and to refine them. Meanwhile, developers need to grow accustomed to these technologies instead of simply focusing on them for their PC games."
All of this is speculative, of course, but it comes from a place of knowledge; Digital Foundry knows gaming tech inside-out. It's an interesting analysis of the situation, and we'd again encourage you to read through the full piece for Leadbetter's comprehensive analysis.