Ultralisks are supposed to be this big scary Zerg unit in late game. However due to their pathing problems in movement they are usually unable to even land a hit on their enemies and get kited + hard countered (by Marauders, Immortals etc).
Ultras are melee units, so they are almost exclusively paired with lings and banes for upgrade maximization. But in combat they are often stuck behind lings and banes, derping around, because lings obviously have faster movement speed. At present their role seems to be restricted to only be “tanking”. i.e. drawing enemy fire their way, tanking widow mine hits, and paving the way for the “real damage dealers” - lings and banes.
One way to make Ultras actually more viable is allow them for movement stacking on top of lings and banes (like the Colossus). It doesn’t need to stack on all zerg ground units, just lings and banelings. While it’s true that Ultras can stack on top of lings while attacking, as we often see vs planetary fortresses, the problem comes from their inability to even reach their target. Having them stack on top of these small units can definitely improve their pathing, their derpiness, and actually reach their target for at least a swipe of the Kaiser blades.
And if this change makes them too powerful, Blizzard can remove the speed upgrade.
As seen in the HOTS cinematic, Ultras were stacking on top of lings while assaulting Mengsk’s fortress. Make it happen!