I really doubt that they're going to include a minor quest simply because of the way the game is structured. It would have to be available in some form at every point in an act, and each act would have to have a different one. I don't see them devoting those kinds of resources to it.
As far as ways to fix it, I think one way to at least improve it would be to make the oath and the things that would break it clearer. I'm pretty certain that every player who doesn't know about oathbreaker ahead of time will break their oath the first time they play a paladin, for one specific reason above any other - they don't even know what the oath is ahead of time. The fact the game doesn't lay out the oath when you pick paladin and you only find it if you read the description on the paladin armor set immediately tells players that the oath isn't important. So they won't take keeping it as seriously as they're meant to.
As a related aside, in Pathfinder 2e they rework paladins quite a bit. Paladins become a subclass of what's called a Champion. Champions are just that, champions of their god, and they're broken down into different subclasses for each alignment besides true neutral. Paladins are the lawful good variety, redeemers are neutral good, liberators for chaotic good, and you can pick any alignment that your god allows in their worshippers, and the advanced players guide introduces the Champions for evil deities. Each variety has some unique abilities, as well as different tenets they have to keep to.
