im okay with them adding a new leader that uses those units. i dont want them to change the current heroes. they're great as is to be honest. not being able to upgrade marines to odst allows the odst to serve a different purpose (they're the equivalent to the sabatuer from command and conquer.) you drop them in behind your opponents base and then set charges and can literally 2 shot a turret. then you can still have your marines being cheap base and vehicle repair units.
im sad that the elephant isnt in the game, but i dont want it to be a base as it would defeat the point of mini-bases. just a mobile garrison. i hope it gets added along with the cobras and hawks. there's also the mongoose and rocket pod warthog as well as the mammoth and the mantis the carrier warthog the longsword etc. that arent even in the game though we know they exist. i would love to see a corvette or something be a super unit. im tired of scarabs and condors. i wish each leader had a unique super unit. the albatross would be interesting as an air version of the elephant.
as far as covenant and banished go HOLY HECK ARE THERE A LOT OF UNITS NOT BEING USED, jackals, vampires, spectres, brute prowlers (should have been an obvious vehicle)
dont even get me started on forerunners, drones, flood, and the rest. sure they may not have anything to do with the story, but im not playing the multiplayer for the lore and story. how the heck does playing 3v3 with everyone as cutter or whatever stick to the lore? i played the story and understood it. now i want to play multiplayer and not be limited by the same content. that's the point of dlc. to keep the game fresh an new. adding in heroes with 95% same units gets old after a while. i want a leader that really really really shakes things up. like a new faction or something.