The new GNATdoc is available, let's create a `docs.ada.dev` website (mabye?)

Sure! I prefer completeness and a central place over homogeneity. If automation can bring basic documentation for APIs, that’s perfectly fine and desirable. But IMMO other levels of documentation could co-exist as well. For example for requirements, architecture and design (UML diagrams), testing, proofs, etc…
You want something as automated as possible, I’m thinking in something as open as possible. Combination of both ideas could be great!