Will Punk ever be a big draw? It's hard to say, no one can predict the future. However, the problem Punk has is his size (and his look, but let's just focus on size). American fans want big guys, guys who are larger than life and not someone who looks like a person they might find in their local tavern in a bar fight. If a person were to see John Cena walking down the street, they'd notice how big and strong he looks, and would proceed with caution. Punk doesn't instill that same measure of awe. When you go back and look at the draws in WWE history, the closest you can find to a CM Punk is Bret Hart and Shawn Michaels, two guys who were never strong American draws. In fact, HBK headed the WWF at it's worst ever financially. The biggest draws in modern day WWE have been the Cenas, the Batistas, Triple H, the Rock, Austin, Hogan, Andre, etc. The guys who are larger than life, real life superheros. Punk just doesn't have that going for him. Some of you might point out Rey Mysterio, but Rey is a draw for little children and Hispanics, two demographics Punk will likely never attract.
In Punk's favor, the wrestling world seems to be changing. The Internet is causing all sorts of havoc with the business, wrestling seems to have more mainstream acceptance for the business it truly is than ever before, wrestlers are not animals in a ring but rather professionals doing a job, etc. Additionally, the flavor of wrestling has changed from one of a realistic style to one which attempts to capture the ADHD attention of today's TV viewers. In that, Punk has his chance to leave his mark on the business. However, history would tell us it's not a wise bet to make in Vegas.