We know there's almost certainly a new Dwarf Lord With Shieldbearers model coming for TOW (much bigger base size + three Shieldbearers instead of two), so it could end up being that. However there's always the possibility they could slide in a Dispossessed Underworlds or Warcry team? Maybe even a Hero just to reinforce that Dispossessed aren't going anywhere.
I don't think it's Grombrindal's axe, just because the it doesn't line up with previous artwork, models or Total War and it would be a pretty obvious giveaway - or course, they could have redesigned it, especially if it's for AoS.