I don't think you guys really understand what Naruto is. Here is why Gurren Lagann will never become the next Naruto.
1. It will never be a show with 200+ episodes
2. It will never be as popular as Naruto. Ever. The Naruto manga ranks on the top graphic novel sales list almost every week.
Maybe it'll become the next Cowboy Bebop except with a younger average fanbase. If that does happen I could care less, I don't judge a show by it's fans.