Hi. I'm in the unfortunate situation of having had a potential narrator cancel due to your TOS. To see what all the fuss was about I decided to read it over carefully. I have to say, I think the following is over broad:

"You grant Storium a non-exclusive, transferable, sub-licensable, royalty-free, perpetual, worldwide license to use, copy, publicly perform or display, distribute, modify, and translate any content you post on Storium."

This sounds an awful lot like you can sell the rights to use our created content to a third party ("transferable") without paying anything to the creator even if you sold it at a profit ("royalty free").
For example, you could sell a story to a movie studio as long as it was a non-exclusive license (as the creator also retains ownership).

Now, this is probably not what you intended. You probably just want to be able to use bits for examples, advertising or some such. Moreover, as I'm not a professional writer, I'm not all that worried about people using my mediocre content. However, if I were a publisher of nearly anything it would worry me. For example, suppose I write source books or scenarios for games. I write something I like and later decide to incorporate into something I want to sell to a game company. However, I now have to tell them that they can't have an exclusive license to the part I wrote on Storium, because I've already given a very broad license to Storium through the TOS. Thus, I can readily see why some are concerned.

If I were you, I'd also consider whether or not some European court is going to decide that your policy violates their standards for IP licensing or the right to be forgotten (can't delete own content, there was a recent Facebook case on this), or some such thing. Please consider this issue carefully with appropriate IP attorneys advising you.

I think you have a great idea here, but do be careful and keep the licenses as narrow as possible to accomplish what you need to.

Aaron