Rather than limiting/tying fighter stances/special powers to specific fighter backgrounds, I think it would be amazeballs to instead give Fighters a similar system to monk stances - timed minor buffs that allow pure fighters to use various combat maneuvers and fencing styles, acquired via in game manuals much like Monk Runes.
These would be pure fighter only and represent trained manuevers, exotic fencing styles, and dedicated military training.
Fighters already have a really nice set of perks that would need to be totally rebalanced just for something new and likely somewhat repetitive.