Personally, I think the Grunt Goblin from Halo 5 Firefight Would make a great new leader for Halo Wars 2 Multiplayer.
The Goblin would be piloted by a Grunt Commander, either unnamed or otherwise.
Since there are two types of Goblins, according to the Wiki, The Normal Goblin and the Beam Goblin, both should be added.
You would have the option to build either one or the other, you will NOT be able you have both on the field at the same time.
Both can have individual upgrade paths. They would both have their strengths and weaknesses.
One Goblin would be effect against Infantry and Air units and not as effective towards Vehicles and Buildings, vice versa with the second goblin.
Army effectiveness could either be balanced over all types of units or be tailored towards one or two types of units/strategy I.E. Boosts effectiveness of infantry and light vehicles like Ghosts.
Grunt Squads have shields and lead by Elites.
Jackal squads as a sniper/scout unit (Would replace the Elite Rangers). Special ability could be a holographic decoy.
This is obviously not the final vision I have for this idea, but it is all I could currently think of.
If you like this idea and would like to see this in-game please feel free to give feedback and suggestions. Thank you for reading.