Granted, it would be cool to see the other series run a dirt track, I honestly can't see it happening.
Main reason being, we all look forward to this one truck race all year. Throw the other two series is and after a few years, it'll become "just another race". The Mudsummer Classic is an exciting and unique race, because it's it's unique. It's ment to be a special event; adding the other series ito would kind of overdo it for me. Sure, I'd love to see it, but I can't see it happening.
Not to mention, somebody would complain that the race is favored to guys with dirt expeirience, like Larson and Stewart, where as guys like Biffle (LOL) and Johnson might struggle. (I don't know who exactly has dirt experience. Just picked names that sounded right.) You know with the level of competition that's in the Cup series, some team would complain that this guy has an unfair advantage or they can't keep up.
Besides, we have thousands of local dirt tracks around the country. The racing didn't look all that much different than what those run. Heck, you'd probably spend less money seeing a spring car race at Eldora on a random weekend, than going to the once a year truck race there.
Just my personal opinion, though.