Why not just make her Live-Action Captain Britain?
I obviously want Brian first, but the Captain Britain Corps give you the opportunity to tackle anything and everything. Bring her in at some point as some AU's proper Captain Britain, superpowers and all. Maybe with a nice symbol in the centre...
Also, per F&WS
Falcon's turning into Cap properly. It could be cool, I suppose. I always liked the suit in the comics, busy as it is. And Falcon's such a boring character that anything would be an upgrade. Mainly I like Mackie so I'm cautiously optimistic. I won't lie, I was rooting for BuckyCap because I loved the book back in the day, but MCU Bucky is nothing like Brubaker Bucky, and they've wasted all the good Brubaker stuff, so... Bring on FalCap.
You know what would be cool? If Evans kept playing Old Man Rogers, and also came back properly as a mix between Captain HYDRA and Red-Skull-In-Cap's-Brain from Captain America Reborn.
Good call on Captain Britain! Peggy as CB would be good to see as well.