I think the (r6477) comment just means that the information was accurate as of r6477, although maybe it could mean that it only works in r6477 and newer. Either way, you should never use anything as old as r6477. Just use the newest development version from https://dolphin-emu.org/download/.
Also, it's still possible to change the graphics backend, it's just not called plugin. You can choose between OpenGL and D3D11 if you're using Windows.
Also, it's still possible to change the graphics backend, it's just not called plugin. You can choose between OpenGL and D3D11 if you're using Windows.