@kei and @gandhiano, go ahead and check out the links at the bottom of https://pantheon.io/decoupled-cms . I appear to be less frightened now, thanks to this recommendation from an old id22 WordPress friend.
transformaps.net exists now, we may want to restrict this experiment to a
blog subdomain of such, whilst the FQDN should remain reserved for uMap. Then,
blog.transformap.co remains open for something else like KeystoneJS for me to play with (even though it uses MongoDB).
transformap.co could be upgraded to use Hood.ie and we had a lovely testbed with a nice mix of architectures, programming languages and databases to investigate and costabilize, in other words federate.