With all of the big shifts imminent in Magic 2015, the planeswalker lineup is mostly familiar. It seems as though all of the Lorwyn Five 'walkers will be in the set in one form or another, with the addition of Nissa. However, what cards they will be represented by remains a mystery - though pictures of the Spellslingers web series hosts with playmats with new art of Garruk and Jace shed some light on the situation.
The Garruk playmat has the art from a card related to Garruk but not actually representing him - the rare black sorcery In Garruk's Wake. The Jace one, meanwhile, shows the mind mage floating in front of the Tablet of the Guilds on Ravnica, meaning he's shown in his capacity as the Living Guildpact. The fact that the Garruk playmat doesn't have planeswalker card art on it means the Jace art doesn't have to be on Jace's Magic 2015 card form either; but it does show that his latest canon adventure in Return to Ravnica block will be reflected in his personality in this core set.
The fact that one planeswalker in the set seems to be referencing Innistrad, and the other is definitely referencing Ravnica, means there are likely further homages to past planes in Magic 2015 to a degree not seen at core before.