Really strange situation with Skyla, I'm gunna agree with the theory that it was just a way to milk money out of his audience, or just a really fancy paywall like you guys said.
Somehow I doubt the fan support in 20 days (between his first post asking for support and the second one confirming the story is going to be finished) or at least enough support to warrant him finishing the set.
I think Skyla's sets do sell well, or at least consistently or else he would've abandoned her a long time ago like Miriam. But like all characters, they get stale, more fans start pirating, etc.
If he's comparing Skyla's sales to new characters I feel like that's a mistake. Like a stated previously, new products/characters always sell more than consistent. The only way to have constant high buy rates is to continuously create new characters, but that hits a roadblock if the character isn't well liked, and puts off fans who buy your work for specific characters.
At least we get a set in 2020. Cya then! Skyla's preview looks hot!!!