Followers...

[Psynyx]

Something that I think would be a pretty cool idea for the followers - when you hover over the follower while in the garrison they are outlined in the color of their current rarity. Green - common, Blue - rare, Purple - epic.

[Soliden]

Would be a cool addition but I think it would interfere with their current system of having blue be party members, etc.

[Sidewalker]

I agree with Soliden. Although, maybe they could do something smaller like changing a peripheral color?