Gene, I was happy to elaborate a bit more on intentionality, but I fail to see how you could fairly read the following as some sort of need to intuit the intention of the author (if that’s how you were reading it):

when I explicitly stated that interpretation is needed to postulate the degree of mainstreamness. But, whatever, it’s clear now, I trust. We seem to be on the same page except for:

Where I’d suggest that the mainstream can be changed by encountering subject matter that isn’t typically dealt with in its purview. If this external subject matter were merely latently mainstream all along, then it would rule out the mainstream ever being able to really change. But perhaps you're thinking that any change in the mainstream is some sort of self-actualization in which the avant garde is dregged up from a communal unconscious. That doesn’t seem right to me (like my mom really loving free jazz, but just not knowing it yet), because this would just be question begging. That is, if the avant garde is just latent mainstreamness, then where are the collective avant garde predilections stored and how did they get there to begin with? If all of this is starting to sound like an anti-platonist screed, that's because it is.

Thus, to answer Shoe’s [oops, meant Sock] question (even if it wasn’t addressed to me):

External subject matter (or form, style, and whatever else might reside outside of the prevailing attitude) would become mainstream at that point when it is no longer external, but internal to the mainstream. This is one way that the mainstream changes, by getting used to what was once “otherness”. I’m not sure what genre has to do with it, though, since all of this could and usually does happen within most (but I’m not sure all) genres. Additionally, I'm not sure why you use 'entertainment' here since it's often synomous with 'mainstream' or at least a primary criterion.

I think that perhaps what the public might accept with animated fiction might be too visceral (for public taste - ala mainstream) if done with movies, and most likely illegal if done in a "reality" setting like the "JACKASS" stunts.

If done in a reality setting, such as the STEVE-O movie, DON\'T TRY THIS AT HOME the "art" obviously crosses the line from fiction to reality. The JACKASS movie made more that $64Million at the box office before DVD rentals.

If portrayed as fiction, would this be as popular?
Probably not, but it's unclear. True this may be a "fad" in entertainment. (always around, popular in recent times)

But the same entertainment that borders on the "socially unacceptible" "reality" MIGHT be considered differently if it was apparently fiction.

The fictional "reality" movie that was the "BLAIR WITCH PROJECT" was reportedly initially popular because the rumor was started that it perhaps WAS real. Great gonzo marketing that worked.

Blurring the line between the fictional entertainment and the "reality" shows should eventually reach the point where real people are harmed, obviously.

We've heard of the kids that die trying the "JACKASS" styled stunts.

Many of us have watched car chases in movies, and some have watched the police video-ed chases on FOX...

At one point there may be an opportunity to watch a crime in progress from the point of view of the criminal. "JACKASS WITH GUNS" if you will.

Most would consider this unacceptible entertainment. Not even entertainment.
Yet it's only one "reality" step away from "PULP FICTION" and it's entirely possible with today's technology that this kind of product is made.

What was THE THREE STOOGES is today's JACKASS and what was PULP FICTION becomes tommorrows' ... ??

Perhaps I am not being fair, making the leap between fictional entertainment and reality entertainment. Most people are comfortable reading about killers after they're in custody. Until then it's still probably considered news.
But what would happen if OJ Simpson decided to write the tell-all of all celebrity tell-alls?

Unfortunately, that would be considered mainstream. I shudder to think of it, but the possiblity does still exist. The "notorious" criminal aspect will almost always be so.

But when the average (previously unknown) creator wishes to become "notorious" you end up with reality based shock event entertainment.

You get mainstream exposure, but a cult following.