I’ll throw some points in, just for fun!
-Make cosmetic unlockables from the Campaign/Ghost Mode Special Operations carry over. Currently, you can’t wear items from Tier 1 mode (Operator Bandana, etc.) or Special Operation rewards (Caviera’s gloves, etc.) in Fallen Ghosts (and I assume Narco Road) until you meet the requirements in said expansion (which is impossible).
-Add Los Extranerjos to the main game & Ghost Mode when you have a Unidad Patrol level of 3 or 4, and have them as standard enemies in Unidad bases.
-Add all the new Drones & Skills to the main game/Ghost Mode.
-Add Tier 1 mode to Fallen Ghosts, with drastically reduced XP requirements to reach each Tier, or start at Tier 10 instead of 50.
-Team customization in Fallen Ghosts.
Obviously, this only applies to those who bought Fallen Ghosts.