As to the code standards, my problem isn't with the CONTRIBUTING.md; that seems fine. It's how people make long term suggestions about fixing lasting problems. As an example people who suggest refactoring large sections of Julia's expansive base library (1600 symbols? a problem that causes parts of the slow startup time and memory usage) into other libraries (which would improve batteries included, etc. features) are summarily ignored / shouted down / (predicated on my previous paragraph) banned. Important improvements to the language go in circles (often on JULEP tagged issues) especially any large improvement that would require multiple people and lots of dev work and seem to gain little traction unless a core dev just takes the time to just do it; rather than a timeline to reach consensus and then design a plan for implementing it.
As smaller examples. There was a push to increase test coverage and then months later commits plummeted the code coverage numbers and no one seemed to care. Sections of important code are uncommented, undocumented, and (mostly) untested on purpose. There are modularity problems and software architecture limitations inherent in the language design that go unaddressed. Unpredictable un-typed exceptions, namespaces/modules being hard to use for non-trivial designs, "interfaces" that aren't really. And these are just the ones without serious work behind them I can remember off the top of my head (the debugger and threading I acknowledge being worked on seriously). Though things being worked on seriously suffer problems as I mentioned earlier.
Issues like these cause many of the original poster's problems. Julia is a great language, but the community seems unable to take the steps it needs to to actually make a "Tier 1" general purpose language (e.g. like python, go, clojure etc.). Setup a serious set of policies regarding language proposals; setup a transparent community policy and actually follow it; acknowledge that certain development idiosyncrasies aren't going to fly anymore; take software architecture concerns seriously; remove the toxic core language dev (that to my count has cost you at least 4 serious contributors if not more).
Julia is likely "slowing down" relative to the expected development (which many people have observed) likely (by my thinking) because it is failing to attract/retain the developers it should be as a promising language (in my opinion) because of it's poor development and community standards.
But hey, these are just my suggestions, I don't have any skin in this game. I just wish Julia was as good as it promised to be, and I'm a bit bitter it isn't for human, rather than technological or financial, reasons.
Edit: Sorry I expanded, it felt unfair to not be more complete about it.