Regarding different types of docs and how we can sustainably maintain them, we’ve considered this and put in a recommendation in our Developer Docs OEP. We can update the OEP if folks have a desire to merge it with other ideas from the divio blogpost.
Other considerations, like co-location with code and aspects of tooling are also in the OEP. It would be great to amend the OEP with further principles as you have here that we think are useful.