So today I spent a lot of time on the track. First of all when I opened the project for some reason most of the materials were messed, I had to do them again or edit them it took a lt of time, however, it was good chance to rename objects, so I renamed them, removed all capital letters, unnecessary suffixes, blender suffixes... At the end even though my project for some reaon was messed up, and I nearly had to do gJed work from the bottom again, it was all good, because I somehow lost some annoying issues such as issue #4, so now skidmarks and road/grass transitions are +-ok.
Now the remaining issues to fix before working further, or before posting a test version link for those who would like to:
#1 issue, still have it, but I haven't tried to work with AIW since then, so... work on the aiw
#3 probably shouldn't count on this, though new gJed version would probably make me as happy as new rF2 UI

#5 still not happy about some shadows;
#8 cars having replaced textures, I have no idea what causes that;
#9 didn't manage to get grass to have at least as proper color as before, so grass texture colors
#10 match vertical grass shading and color. Even though I was able to point normals up with 3Dsimed, the lawn around the track still looks more like littered;
#11 find out how to solve issues with multiple UV channels not working in real road shader and multi layer grass/dirt shader, right now can only ignore it.
There is one recent issue... I have separated all foliage from my main track objects. I wish to do foliage separately with gJed, but I think I am not going to touch it for a while not to break main gJed project, I wonder if I already broke XJ13 gJed project.
One kool thing ! I tried rain and it works great, except that wetness appears warped, but it works, it builds up, it dries down as I drive, and later when it is dry, rubber builds up too. But because UV problems I can't fully utilise it all.
I also had mad fun with XJ13 in the wet, kinda felt like Kenny Brack with GT40, though I went a bit faster than him, then I reduced wet grip a bit, but I still was faster. Then I remembered that viscous hydroplaning is not in effect, so I don't have to use longer lines, adding to that dynamic hydroplanning and puddles aren't really presented in rF2 so I suppose I could add 6-8 seconds to my laptime (1'44), and then it seems fair.
But how fun it was, car is very twitchy, but handles well if you just go through it, car speaks fast at front and rear, they are loosing grip at different times, loosing it quick and regaining it quick as well, car is wobbling, very believably, you can get nice powerslides if you carefully press it down, but you can't abuse it, have to do a lot of control with throttle...
Overall I am quite happy with physics work on the car so far, even though much of it is not based on any data, mostly on feel, I feel like it is a good way too. I also for the first time feel like rF2 wet physics are actually really good, despite lacking few important elements. I feel like some cars in rF2 in rain has something wrong the way they act on the balance point between sliding, and having grip, maybe front tires usually lacks grip when car is accelerating, so you can't fish the rear end out of the slide because front and rear startst sliding, even though at first only rear end should slide ? I find that I usually want to give front tires a bit more grip, even though they are not so wide.
Just to compensate lack of media in this post:
Wet stuff related. Always has grip at the front, rear slides doesn't kill immediately, and can take quite a bit of angle, and stay there. It was sideways forever at 1:39, I am not sayign that it is easy, and safe. But try to do that with M23, you will not make it. It will probably fall off super fast.