I think everyone here has great points and very valid points. My take on a Forza level livery editor is naturally very pessimistic, and this is all based on the fact that PD has no plans as of now to implement one. If it ever does make it in, I wouldn't be trying to pound on it in the forums.
I just want to clarify that I am not saying "livery editor = penis cars", but rather the implementation of such a feature will open the flood gates and you will see all kinds of good and bad stuff. I'm sure penis cars and pin up cars will take up only a fraction of the entire livery marketplace, but personally (!) even a 4:1 of good-to-ugly liveries will make my experience sour.
I'm totally aware of the fact people do stupid stuff to their cars already in GT5 in regards to chrome paint and weird wheels.
I just want to lay out some examples to give people some context so it isn't just a case of pooping on your party:
Counter-Strike Global Offensive implemented gun paint designs at one point and one of the first things that I see is a bright ass purple AWP with lightning on it. It actually made me go what the 🤬. And then there's another gun with Hot Topic skulls all over it. Believe it or not, it does ruin immersion despite the fact CS is a very arcadey and unrealistic game.
Call of Duty, I don't play that stuff but I know they're selling actual Hello Kitty-esque gun pack. Enough said.
Now here's the most important example that is so ridiculous that actually killed the game and made plenty of people uninstall. Team Fortress 2. In the first year or so, there have been really awesome designs for TF2 hats and items (equivalent of really good racing liveries we would love to see in GT). A few years pass and now we have the dumbest looking 🤬 ever imaginable, which makes up for most players wear in the servers. At its current state, these hats and stuff really killed the game even if there are some really well made items too.
I fear that the open endedness of a livery editor could drag the game down. You could have a grid with 75% really great liveries but those 3 assholes that decided to bring pony cars into the game would upset me just like that. Considering the incompetence of PD, I doubt you can turn it off client-side.
But then again this is just a pessimistic view, opinion for a poll vote because the idea is still up in the air for speculation. If it ever gets implemented for real, I'm all game.