He could be white/blue. If his + ability was similar to narrow escape, i wouldn't be too suprised. I think making an opponents spells cost more during his/her next turn would be a decent middle negative ability. maybe even "until your next turn, whenever an opponent casts a spell, you may draw a card unless he or she pays 1." That actually wouldn't be a bad + ability! And i agree that his ultimate will be the hardest to peg, but i'm not sure it would be turns. That kind of ultimate would probably be best left to Karn, since he is the only known being in magic to travel through time. And since wizards has trademarked a few new names (Scars of Mirrodin, New Phyrexia, etc.) the possibility of seeing a time-'walker wouldn't be completely outlandish. I feel that a Jace in zendikar would be highly specialized, think along the lines of tezzeret and nissa, even the new chandra. A jace that could search up an instant and play it something like "-3: Until your next turn, if an opponent casts a spell, you may pay X. If you do, search your library for an instant card with converted mana cost X, cast it, then shuffle your library." That would seem like the best way to protect a new planeswalker with an empty board. I'm basically at a loss as to what his first and last ability would be, but i could see his middle ability being a sort of counterspell or something.