Just speculating about future units, and I think Waiqar heroes show us that theres a lot more coming.
Starting with the obvious one.
New seige. Waiqar needs a new seige unit, not that the lancer is bad, but because lord V has a useless embedded card currently. They wouldn't make it if it served no purpose. The lancer feels like a technical seige unit, so getting a 'brute' seige would be fitting.
Now moving into the more theoretical.
New Cav. FFG is generally pretty good about introducing things that help a failing older unit. Maro still has no good home for his cav upgrade. Deathknights are definitely heavy cav, so give us high hp, low armor trashcav.
New Infantry. Again with boosting an old hero. Ardus is 'ok' in reanimates, but seems highly priced when surges are still so rare with RRW dice. I'd like to see a specialized infantry like scouts that have roll BB or BR that could make Ardus really sling some surges.
It's all guesswork of course. But it seems like the logical path.