I think that when iron members and non supporters attempt to go to the Utopian wild/nether/waste they get placed in a glass box where you can view what the utopia wild looks like. Enderpearl flag would be off to prevent people from escaping but this is just a viewers platform to show people what would wait for them if they get gold or diamond supportership.
Or even perhaps a trial of the Utopian wild? (for iron supporters only). Maybe like a 1 hour trial to go anywhere before they get teleported to town? Like your idea too.
The wild/ nether on utopia looks no different than other smp's, aside from the fact that it is always day in the wild. Only other difference is no hunger or fall damage.
I like jake_bagby's idea about giving iron supporters a 1 hour trial of the wilderness before they are teleported back to town. That way they can see what they can get if they become a diamond or gold supporter.
We already have the protected zone - that seems like the perfect area to confine them to, if you're going to let them in. But honestly, I don't think letting iron/non-supporters see the wild will do much. At best, it would help convince a few people to become supporters; personally I don't think it's worth the trouble.