Blizzard has announced that players can expect to increase ranks for Ultimate Skills in Diablo 4 Season 6 and Vessel of Hatred! This will increase the damage of those Skills and reduce their cooldown.
Diablo 4 Patch 2.0 PTR Notes
Blizzard
Ultimate skills can now have additional ranks. Players can invest up to 5 skill points into their Ultimate Skill, and bonus ranks of Ultimate Skills now exist. The limitation of having one Ultimate Skill remains.
