Nothing. I dont understand livery editors. Devs spend weeks and months designing cars and liverys. Why let people make their own liverys? It would be better to have Liverys added to choose from then add our gamer tag names to our cars and thats it. Also no more achivements for Liverys created, its a racing game, to race, not mess around with decals etc lol
But Gran Turismo is not just a racing game, and never has been. There was always the need to pass the Licence tests, not needed in just a racing game. Tuning of cars, not needed in a racing game, and indeed most of the people racing online don't want that aspect of the game included in the online racing. With your rationale even changing the colour of a car is not needed, as for you PD offer everything. Try a one car type race of say the WRX STI Isle of Man Time Attack Car and everyone uses the default design. Which one were you in the replay!
If I were in such a race my car would be unique.
And dare I say better than the stock design imho.
A photo mode, either taking pics in a race replay, or of a car in a static scene. Again, not needed. As time has moved on PD have added other aspects like these to their games because they realised that just a racing game may not hold users attention for long, and indeed may not offer value for money for a lot of people.
As for the Livery Editor in particular, people use the Livery Editor for a multitude of reasons, but I would think there are a few that stand out, and the first one is that, to stand out from everyone else. Another is whilst the designs of most of the cars are very nice, you could be in a race and someone with the same car could look exactly the same. May not matter to you, but it does to some people. Were there are teams in real life that may have two cars the same design (though there are normally slight differences to differentiate the drivers cars, something the game does not do), having up to 16 cars looking exactly the same does not make for an interesting spectacle from the outside.
Some may want to express their creativity, something just a racing game could not do. Some may be part of a team that race together and want to have a design that shows they are part of a team by having a team livery. I personally want designs that are made by me, and how I want the cars to look like, that are unique to me, although I occasionally try to replicate a real life racing teams livery, that is not in the game by default, as accurately as possible.
As for making livery's, and other aspects of the game not being in the achievements, it is more of an achievement to create something, be that a livery or a photo, than having been in a race a certain number of times, or using the game for so many days.
The good thing about adding all these things though, is that you don't have to use them, they are optional.
And btw, I don't understand the reasoning of posting in a thread about a part of the game asking for ways to make it better, when you have no interest in it, and by the sounds of it, may have never used it, and probably never will. How is that adding to the thread in any positive way!