This is just one of those vague half baked ideas that come to people now and then, usually they're nothing, but occasionally something good comes of one. I was looking at the objectives and just had an idea for objectives that are used against specific factions only, and generally kept secret till the game ends. written in a sealed envelope, for example.
Some ideas i had was one where you have to have a certain character kill a space marine in close combat and survive to the end of the game, the objective was collecting a gene sample from his or even a progenoid to learn about the marines current genetic status. Might be good against primaris.
If fighting ig you might have one where you not only destroy a tank but place a special demolition charge on it to utterly destroy it so there can't be any fuel. armor or parts salvaged thus having more effect on the guards long term tank forces. Or kill a specific character like a commissar who is notably good at keeping troops in line in some really gruesome way, like with a character of your own.
Against nids you might have some collect genetic data objectives. Nids might have an infect enemy forces one somehow.
Basically a list of each faction and maybe 3 objectives to achieve against them that are recorded secretly.
Yeah, some of you will love it, some will hate it and maybe a few will discuss it. Let the dice roll and see what happens.