What would need to be changed? Core idea being that anyone could sell their soul to demons/Devils for power.
I think the only changes would be that they cannot be resurrected, and their souls go to hell/the abyss regardless of alignment. Maybe to balance it out give their weapon the unholy quality for free. If they fall to evil let them convert into regular antipaladins.
Any other problems/ideas?
Seems like an idea/trope that pathfinder is lacking.