All I can say is when they come out with Blizz All-Stars I will play it. I already play LoL, but a MOBA by Blizz is something I'd be interested in trying.
Basically I don't think you can say "this market is oversaturated", because look at the MMO market...I would have called it oversaturated years ago, and yet here we are in 2013 and there are STILL big MMOs coming out (Elder Scrolls Online), and probably a bunch of smaller ones I don't even know about. I think there's definitely space for Blizz All-Stars...it's not going to earn as much as their other franchises, but it's still going to earn a lot.