Yeah, I read about that, but the non-availability of Sebastian Stan to reprise the Mad Hatter is a problem - who else could anchor that series?
The plan is to center it on Alice, a character they haven't even cast yet, and is definitely unproven as to drawing power. Stan is just one of those actors who can inspire an insta-cult following. There aren't too many like him around. They should cast and introduce Alice on OUAT first, and then see if she inspires a following. Then they can think spinoff.
On that topic, Disney now has a hit movie in the Oz-verse. Maybe they could do a spinoff series based on that?