I think GP is different enough that he warrants a traditional skin. See I have a friend that I used to play LoL with all the time. GP was one of his favorites. He used to chant all of GP's goofy lines like "Yo ho ho and a bottle of... RUM!!!" and "Nothing but a buncha bilgerats!!" And the most memorable thing he used to do was on champion select I'd always ask "So who are you picking?" and sometimes he'd turn at me and smile and turn up the volume and then shout "PREPARE TO BE BOARDED!!!" as he clicked on GP. Upon seeing the new GP voice over though... you could not even imagine his anger/disappointment.
All of that part of GP's character is gone. His old Ultimate laugh. His old "pirate mc piratey" lines. Everything. The gameplay side of the update is undeniably better than old GP since you retained every single old aspect of his kit and enhanced them, unlike other reworks, but if you could please just do GP players a favor and give him the traditional skin he deserves, that would be wonderful.
I know Sion didn't get one because yall were embarrassed at his entire character being a parody of Arnold Schwarzenegger and didn't give him a traditional skin because it was worth abandoning the old personality, but GP despite being a bit goofy was really jolly and charismatic. I don't think that's anything to be ashamed of.
At the very least, take his current model on live and polish it up and turn that into the traditional skin. Maybe rig it to the new skeleton of the new model. Have his old champ select line be shouted when he spawns at the start of the game, and keep the old VO in general and let classic GP fans at least keep that aspect of him.