This is a very thorough and concise document which focuses on the right problems, whoever authored it did a great job!
One thing that I feel is missing is enabling volunteers. Currently volunteer developers are not empowered to do effective work; IMO the main reasons for that are lack of documentation, lack of support, lack of training and mentoring, and lack of code review. Documentation is called out in the relevant section, code review is sort of mentioned (although the phrasing suggests that issue there is lack of automated testing, and for volunteer patches that's not the biggest problem by far, but unclear and unequitable code review responsibilities by paid staff, and lack of agreed-on review processes like SLAs), but support (in the sense of e.g. mediawiki.org's support desk) and training/mentoring are not. Those are IMO fundamental to volunteer capacity building (they affect paid staff too, especially during onboarding, but they have easy access to informal versions of most of those).
There's also the issue of the high learning curve of our development tools (Gerrit etc), although one could argue that we can't realistically make much dent in that. Standard developer environments are mentioned, but usually that's meant in a narrower sense (stuff that runs on the developer's computer).