So, considering that we have 4 regular whacky humans obliterating armies of the undead, and also the beast of Nurgle which in the lore is strong as hell.
If the Fatshark ever adds a death guard marine as a boss, they should also consider adding a new class which would be an Astartes Neophyte that went under the first stage of their genetic transformation and sent on a survival training to Tertium.
That would be a cool introduction story to the new class since space marine chapters send their Aspirants and Neophyte on survival (training) missions all the time so that they can either prove themselves or raise their status within the chapter.
At the character creation screen, we could pick the chapter as the background story, and then the gear would be designed behind that choice as well as the dialog.
Probably they will never add something like this but it’s just something that I had on my mind.