That sounds great in theory, and has been discussed in another thread.
But as came out there, you have to keep in mind at least two limitations:
- you need writers to create such documents;
- and you need those documents to be kept up-to-date with the latest version.
Especially the latter is difficult in FOSS. Just look at the number of programs that simply disappear because maintenance stops, or the amount of documentation you find in general. Already dt provides documentation that is (far) above average.