Considering that 343 and CA said the DLC leaders do not need to be canonically involved with the plot and that Admirals Preston Cole and Xytan 'Jar Wattinree were the top strategists of their respective faction. Wouldn’t be cool to have them on the game? Given that they’re both dead now I think this would be one of the few ways to see them on a game, the others being spin-offs games or retcons (which seems more unlikely).
I don’t know about Cole, but I would like to see Mendez come with a bunch of Spartan lll based abilities and Rtas Vadum/Sesa Refumee come with something. Probably spec ops Elites