The only point of contact you would have is developers@twitch.tv but they will likely tell you the same thing I have, that there’s a queue and your Extension will be reviewed when possible. Anything from staff holidays, unusually large queues, Extensions that require the review team to consult with Twitch Legal or other departments, can all substantially increase the review time.
The exact process by which Extensions are reviewed is not publicly disclosed, all we know is that there is a review queue and the review team will email you if there is an issue.