Re: Villains You'd Like to See Return...?
In an OT line-up, I wouldn't mind Deathstryke (I hate how they spelled her name in the film) coming back. If done properly, maybe she, with surviving remnants of Stryker's forces could form the Reavers. With no mind control, they could establish a past between Deathstryke and Wolverine. I would love to see the tragic romance of TAS introduced.
In a FC follow up, An expanded Hellfire Club, introducing the inner circle of Shinobi Shaw, Selene, Gamemaster and a combo of the Upstarts/Hellions as a field team. Rework the Younghunt story into the Upstarts/Hellions targeting the X-Men and Brotherhood over the fallout of First Class.
Different Brotherhood's. Mystique and Toad have had their own teams, why not introduce them in the movieverse. Maybe Mystique has taken over at different times over the years if Magneto left every now and then. Or after the OT line-up, a surviving Toad launched his own team to continue Magneto's work or his own agenda.
New Villains: If they expand on WOlverine's history, hopefully in a WOlverine film over an X-FIlm, Omega Red Please!