I personally would like to see some type of open world-esque type of ME game. One where the city below is accessible. This introduces more street parkour which gives players more variety.

Imagine Faith doing a cannon ball into a limo and escaping Kruger-Sec. Maybe a new city entirely? They could introduce Faith to other runner factions that she could join based on their own values. If she's given a choice to choose between two groups, whichever she winds up joining, the other would be her enemy. This gives us more types of enemies.

I think a multiplayer aspect could be incorporated too allow parties of players to roam the city together to complete co-op missions. I literally just made all this up while eating cheese crisps wallowing in my wits since another year passes without ME. Sad face.