Most likely both. As Chaos Sorcerers and other such special roles will be requisitioned, it would be awesome to see possessed chaos marines as a requisition-able class.

If there would be an option to mutate your hands into weapons...

I feel like this HAS to be in the game for Chaos to make it seem more...Chaos-y....

I care not to be mutated in a deformed way but having daemonic strength and their enhanced scenes would be good too. Also having a squad of possessed marines under my control would be awesome as well.

If there is a class system where you start off as a standard marine, work your way up to Havoc, with the final option of Obliterator that would be something.

The game can only lose if there are no Race-specific perks/traits. Given that Chaos Legions are unique with how the gifts of the gods affect them, I want to see EVERY kind of mutation that has EVER been suggested, shown or implemented in a book.

Well i think Possessed Marines would be a cool idea, it would be a good melee specialist character

Replacing jump packs with wings would be cool.

Hopefully they're like the mutations in the pen and paper game Black Crusade.

I'd love to achieve Pseudo-Daemonhood or have my head eternally on fire. It'd be great.