I guess "maintainer" is something you grow into. It's not assigned from the start. Like any active repo, there is a certain style of how things get done (e.g. coding style, how files are organized). There are plenty of opportunities to practice what is expected from a maintainer, e.g.
(0) use tensorflow addons and find new bugs
(1) contribute as a developer (i.e. create a branch, fix the bugs yourself, open PRs)
(2) code reviews (i.e. write code reviews for other peoples' PRs and give helpful feedback)
(3) fix the PRs of other devs (i.e. fix stuff in their branch)