People are certainly free to fork Go, or any open-source project, and take on the roles and responsibilities of Maintainers, but I believe fragmenting the community has almost always led to the overall downfall of a language. Communities are stronger united.
With that in mind, generally Maintainers have the prerogative to decide the specific areas of a project that need improvement, and to focus their time and energy there. Contributors are welcome to contribute code to areas highlighted by Maintainers, and generally Maintainers are responsive and happy to work with those.
Certainly with the volume of PR's (100+) and Issues (5k+), the current Maintainers have their hands full. Decisions will have to be made, and priorities established. While an argument may be made that we need more Maintainers, this is not an overnight solution. A Maintainer needs to really "own" the project, and has to have substantial knowledge of the code inside-out.
Developing a great product like Go takes a lot of time and effort. I believe that slow(er) development is a fine tradeoff for the polished, focused language that Go has become. I would gladly take that any day over a fast-and-furious project where development happens at light-speed but the overall quality decreases with every commit.