Here's why I think this:
1. Voice actor sounds nearly identical to 3's Zolton Kulle
2. Zolton Kulle was always "rah rah humanity and nephalem over everyone else." Lillith is a demon outcast. Even though she may be merely using the nephalem, Lillith and Zolton Kulle would have overlapping interests atleast in the short term.
3. Judging by the dialogue "brother against brother" in the gameplay video, it seems as though humanity has descended into an eternal conflict of its own. I'm thinking this dystopian setting, combined with the interventions of Malthiel and Prime Evils prior to Lillith, sets up the reasons for her summoning.
I'm thinking Zolton Kulle summons Lillith to get the nephalem back on its dominant track. I believe that Lillith, though her intentions at this point are unknown, is going to want to restore Sanctuary and humanity to the state she may have originally envisioned, believing it to be corrupted from the Prime Evils' and Malthiel's + Tyreal's intervention. Both Zolton Kulle and Lillith, though their ultimate goals may be different, believe they must go through same means to an end to accomplish said goals. Ofcourse this "means to an end" is likely total scorched Earth and world wide dictatorship, but it would fall in line with Zoltan Kulle's penchant for machiavellianism. Perhaps they aim to reconstruct the world stone, something that requires other dire prerequisite action.