Riot - Since you INSIST on the Prestige Point system....
For Event passes, give us the option during events to redeem our 1000+ or whatever event currency for any one prestige skin currently available for points, OR the one released during that event. For instance, during Lunar Revel, you could have either been working towards Prestige Firecracker Vayne or Prestige Blood Moon Aatrox. For whatever future Pass event you have planned, that would mean that Prestige KDA Ahri, Blood Moon Aatrox, Fuzz Fizz, and whatever is being released within the event would be purchasable for the currency, so it's not such a bitter pill that things like Prestige KDA Ahri are currently locked out behind spending $100+ on hextech gambling. Then, you can simply put the event prestige skin into the Prestige Point pool for for people to purchase with the Points (if you must have them), or future events. Then, at year's end, you can simply retire ALL of the prestige skins released that year.
I think this is a healthy compromise to this Prestige Point system that you insist on keeping. You get to keep the system in place, you get to make prestige skins to your heart's content, and player don't feel so shit out of luck if prestige skins we really wanted get released outside of an event.
Please consider this option.