Mystique showing up as her Raven Darkholme/secretary of defense persona would fit perfectly and lay the groundwork for Rogue, even the Brotherhood. The Rogue vs Carol fight would be better for the end of her trilogy.

Rogue and the Brotherhood could go on to be a larger MCU threat and lead to the X-Men.

I would love to see that Storm/Wolverine fight with Rogue at the Pentagon in the comics on the big screen one day...