Nothing stops the API evolving... Anyone can make a build of Chromium with a better API, test it out with their own extension, and if it works better, then they can send a PR to get that API into Chrome.

Obviously, extending an API is a long term commitment, so I can understand the Chrome team wanting to only do it if there is a decent benefit - "it makes my one extension with 10 users work slightly better" probably doesn't cut it.