In the past there have been a ton of 520 skins being completely revamped from just recolors to full fledged skins that would be 975 RP according to this Guide to Skin Price Tiers. The ones that come to mind are Shadow Evelynn, Enchanted Galio, Tundra Hunter Warwick, Infernal Akali.
We had to go to multiple twitter accounts and make multiple reddit posts on r/MorganaMains for them to finally say they will make Exiled Morgana (a 975 skin that was previously just a recolor with a different passive and auto attack effect) get a recolored VFX.
Before anyone says "it's on PBE they would have probably changed it" just watch this video [of RiotAugust stating otherwise](https://www.youtube.com/watch?v=83lbpCE2FuM) and I had a ton of issues with almost everything he stated.
The simple fact of the matter is if you do not want to put resources in making a 975 RP skin worth 975 RP then lower the price. The Guide specifically states 975 RP skins "Pushes the champion a step beyond a simple costume change, with more immersive qualities." while 750 RP is just a costume change. Lower the price or update the skins properly. Thanks.