So hypothetically, why would I (as a consumer) want to pay for Star Trek fanfic when there's plenty of free fanfic out there?
I happily pay for a professionally-written novel because I value my time. Its worth it to me to pay for an experience that I know will (usually) be good. Not that all of the fanfic out there is bad. But finding good fanfic is time consuming.
SNW was a little different, in that it was curated. Editors combed through the submissions and only published the best work. I enjoyed SNW, but even so, only a few stories came close to being as good as what the professional tie-in authors create. (And, they were all short story length. Producing a full length novel is a lot more difficult.)
It sounded to me like this concept wasn't even going to be curated, but I could be wrong. (And, curation and editing costs money. Cheaper than hiring a writer? Maybe. But if so then why didn't it replace professional writing already after the SNW experiment?)
All that to say I think that the professional tie in market will continue. They are already competing against free fanfic and so far I'd say a lot of us think it is worth the money.