Hello again :)
I want to add my plugin to prerender, but current config schema doesn't allow it.
Sure, what are you looking to do?
You should be able to add additional plugins to "plugins":  in the config file.
Of course, but i can't add my plugin, because you require it from ./plugins path.
Makes sense, I can update the code to allow a full system path to a plugin file instead of expecting it to be in ./plugins.
Full system path in JSON is not easy :). Why you choose JSON format?
JS in more flexible:
And you can pass the plugins objects to config:
This looks good, simple and flexible