Mightygodking,
Jim Hines,
Chuck Wendig and doubtless many others have already weighed in on Kindle Worlds, Amazon's new thing that'll let fanfiction authors write fanfic for pay. They offer more depth of information than I'm going to bother with so you should check them out if you're curious.
As for me, I currenty have almost no interest in this as a reader or as a writer. When I write fanfiction it's largely for the personal pleasure of playing in that world, and I'd feel weird asking people to pay for it. When I
read fanfiction, it's kind of for the community experience: to satisfy that drive in me as a fan to find other fans who see the canon similarly to the way that I do (shared ships, similar ideas on the world construction and/or magic rules, etc) and want to expand on that. Legitimacy through folk consciousness, or something. That and I'm a fan of multiverse theory, and fanfiction creates a multiverse of multiverses where anything can be true in at least one of them. Which is awesome.
Meanwhile, when I finally do publish something for profit, I want it to be an original work. Not because I consider original fiction inherently superior to fanfiction, but because . . . again, I'd feel weird asking to be paid for something that I feel is so much more community-based. When you write something new, you're the source. You give birth to it, and if you're really, really lucky, a community builds around it. (I am one of those writers who would be flattered, honoured, and thrilled if people started writing fic about her work.) You get final say in what's canon, and the fact that you're the one paid to write that canon is sort of what signifies your godhood in that universe, but the community that loves the work get to dictate the fanon and turn your universe into a multiverse. If you're a really nice god, they'll let you be an active part of that multiverse, but at the end of the day, it belongs to
them: it's built on
their love for your work.
I feel like the pay-for-fanfic system sort of fragments the fandom community a little bit by trying to introduce tiers to that community, that the community itself didn't create. I'm not even fully certain if pay fanfiction would come to be seen as being in any way "more" canon/fanon than a free fanfiction - I guess it would depend on the fandom and the author's/licenser's say-so? - but speaking from my own place of preference, I'm not sure I'd bother reading for-pay fanfiction unless it was a series I'm ravenously addicted to, which lacks continuing canon material, and even then only if the fandom generally approved of it. If the fandom is largely ignoring the for-pay fanworks, I'd see no reason to bother with it myself when I can read equally enjoyable and well-written fanfiction for free at AO3 (or here on Dreamwidth, or on LJ, or on Tumblr, etc.) So the for-pay fan-author is kind of shoved into this much lonelier category, in which they're not really the "god" but not really part of the main community, either. Adding on top of that the extremely limited rights that a for-pay fan-author would have on their work (ie: basically none, outside of basic royalties for putting it out there) It just doesn't sound like fun to me.
But then again, money is nice, so I don't really condemn it either. I'm sort of curious about how successful this is actually going to be, but I doubt that I myself will participate much, if at all, in this new development; either as a producer or as a consumer.