Well, I maintain that Post has a lot of potential as an archenemies for Cable, mainly due to their past connection. Post is a mutant who was being experimented on by the Mandarin, when Nathan saved him and gave him a blood transfusion to save his life. The T-O virus in his blood stream interacted with his mutation in such a way that it seems to have augmented his powers, giving him some unique abilities between his drone-like tech “platelets” and his own natural mutation (which I think is still pretty poorly defined). So he’s a character that a good writer like Ewing could come along and really flesh out and make a very cool villain for Cable IMO.
Here’s his bio:
https://comicvine.gamespot.com/post/4005-15075/
Beyond Post, and possibly a new MLF headed up by him,
I’d also like to see the return of Weapon P.R.I.M.E. as a government task force created to keep tabs on Cable. I really enjoyed the aesthetic of the character Killspree (even had the old Toy Biz action figure they made of him) so wouldn’t mind seeing him, Yeti, Tigerstryke, etc., being recommissioned and hunting down Nathan again for Department K. Those are some additional obscure villains just ripe to be fleshed out more and made into a regular part of Nathan’s rogues gallery.
From there, maybe a team-up with Rachel to fight Ahab and his hounds (since, yes, it’s true that Ahab is really Rachel’s arch nemesis) and also Cable versus Orchis and Nimrod at some point too. Maybe also have him mix it up with some cosmic Marvel villains out there in space too, or even invent some new enemies for him who are aliens. That could be cool.