If they were to bring out a car mod dlc, it shouldnt be named "The Los Santos Customs Update" imo, they should bring back the mod shop from San Andreas and call it "The Wheel Arch Angels Update" especially if there is going to be more extreme looking kits and liveries etc...
We have very similar minds .
I posted this in a thread dedicated to the arrival of a DLC that is practically the same as the one the OP has suggested. The only difference is that the thread used NFSU2 as the basis specifically.
In the thread I suggested that along with all the new cars, Mods, Upgrades (Nitrous and drift tires) and other features that Wheel Arch Angels be reopened at one of the dock warehouses, So the docks has a better purpose than the place where you go to get ripped off by Simeon. It would offer exclusive stuff that is out of LSC's league like Neon, special widebody kits, Special paintjobs (Like the one in my signature) and as an added bonus it would sell the Chrome wheel paint we all very much desire.