Player portraits really need an update, but I say keep the old ones, for they aren't that bad.
I feel like adding Spartans isn't a bad idea. I understand they weren't supposed to be fleet commanders, but it wouldn't be too much of a problem. If that makes some fans happy, why not? Furthermore, Jackals are represented in Covenant's portraits, and as far as I can remember, they've never been Fleet Masters.
Putting in known characters is another idea I don't dislike. I would love to pick up an Arbiter's portrait, or even Rtas. More Prophets, too.