I'm not sure I completely understand your question... But Cyan has always envisioned Uru Live to grow and expand with new Ages, puzzles, and content. And, yes... Ages, puzzles, and content created by Cyan. Now that Uru Live is almost back, we will finally get to experience it! (Many here have been waiting just as long as you have.
)
The only reason you'll see "barriers" is because the areas behind said barriers aren't quite ready for exploration yet... but will most likely become so sooner than later.
As for fan-created Ages... this nearly three-year hiatus showed Cyan the creative capabilities of many within the community. They realized that they will be able to take advantage of that creativity and use it... Not necessarily in a way that will affect Cyan's vision of the actual story of Uru... but, at the very least, accessible perhaps from within the Library to those who wish to explore more of what the community itself has to offer.
Eirerogue wrote:
Will there be any worlds for "the stranger" to explore? For that matter, will there be any exploration?
Yes and yes.