Jace I assumed wasn't for his -12 ability that you use him. Its the other abilities I would love to use. Looking at the top card of any library, and making sure it doesn't get drawn is cool, brainstorm is an AWESOME ability for combo deck players or anyone filtering out their hand, and bouncing definitely still will have its place on the game forcing the opponent to lose some tempo which is seriously what Magic is often about.
I think this card is a huge centerpiece for any combo/control oriented deck, and probably a great place for any blue deck probably in the format at the moment (which appears to be bounce and merfolk based). I would love to make a bounce deck with the new cards that have come out to really compliment this. I'm glad blue is being pushed to use bounce more lately, as its a mechanic I felt of blue needed more attention (and thankfully pulling away from counters more).
Again btw with Baneslayer vs. Iona...Iona is 9 mana to cast (7 plains I guess if you get that land thingy to revive her) and doesn't have nearly as many protections, she gets to stop one color's ability to cast, but I ain't sure how many decks are around that can't slow her down or stop her.