It will only work if they can figure out how to monetize it. There are probably five 'books' out of perhaps 60,000 on my favorite display site that I would happily pay to own, and which I will certainly download when they are complete.
As much as I love using them as entertainment and outreach, I have a few problems with Wattpad, Archive of Our Own, and other display sites. The biggest is the general lack of editing, which distracts me from many stories. I don't care that lots of readers may not be well-versed in English, and so want/forgive approachable stories that may have flaws.
I see the flaws. If there are too many of them, structural or mechanical, I stop reading the story. I can't take seriously a Wattpad author who never edits her work, and posts chapters a few minutes after she finishes them. She's got to be pro-level already, for that to have a chance at working in the long term. In my experience, posting unedited work-in-progress usually leads to overlong, careening stories with many errors. Reasonable revision is a part of editing, and a skill even dilettante authors should know.
I've also seen this on AO3: authors with strong, clean prose tend to attract a loyal readership that appreciates the same. Authors with clunky, immature, error-ridden prose tend to attract readers that will forgive it because they may not know better, themselves.