I'm A Banana
Potassium-Rich
The one thing I know I'm going to do with Backgrounds is make them an additional point for Inspiration generation.
The Background names plus the BIFT system (Bonds, Ideals, Flaws, Traits) when combined together are almost a recreation of the Aspect system in Fate. Your Background is your High Concept, your Flaw is your Trouble, and the Bonds, Ideals, and Traits are other Aspects of your character. And every time they apply, you acquire an Inspiration (Fate) point, which you can use to re-roll a check. The two systems are very similar.
In my stab at Faction Backgrounds for Planescape, I took this one step further and actually let the backgrounds give you interesting things to spend your Inspiration on aside from advantage.
The idea being that PS Factions require some sacrifice and hardship in adhering to their philosophy -- which is how you're going to get your Inspiration. And once you have it, the PS faction background gives you a special way to spend it. So, like, the Free League just automatically make a Wisdom save by spending Inspiration.