The class SHOULD have been called "LM" in keeping with tradition. It's a misstep they took in GTSport.
If it was the LM class, it opens the door to all the LM cars of the past.
Well, It's a game, so....
IRL, they are still mods of the base car. it's just that factories have more resources than a normal person. A normal person cannot just go out and buy a Gr3 car either. It takes serious coin and connections.
The Race cars have different chassis specs. Just as buying the weight reduction mod changes your chassis specs, a race mod would change the chassis specs.
IRL, many racing series will require the car to be modified with a special fuel cell that is fire proof and fits a very specific set of rules.
I would take the simplest route possible, given that the team struggles with the minutiae of some features, and it could be why it's not in the game.
For cars with available race versions right now, the "race mod" gives you the same car, but with no decals. So, for the NEW NSX, GR4 Race mod gives you the GR4 car, GrB Mod gives you the GR B car, GR3 mod gives you the GR3 car, and GR2 mod give you the GR2 car, all without decals. The mod alone would be priced a little less than buying in Brand Central, but more overall, because you have to buy the base car.
But it's not "the same". The visuals are close, but the chassis are different. A RM would give the car the chassis values needed to be in the class, and it would change the designation of the car from "road car" to whatever class you modded it to. So, when a race says "GR4", I can take a Gr4 RM into it.
Most cars allow for roll cages to be added to them right now. This is where it dawned on me that this is not only a realistic addition, but likely part of the original plan.
Most cars can have a wide body
Most cars can have tow hooks added
Most cars can have hood pins added
Most cars can have a roll cage added
Most cars have "racing" parts available to them
One does not exclude the other. It Also allows for more Easter Eggs like the BMW CSL Race car.
Lastly, if this isn't proof that they thought of adding an RM Mod, I don't know what is. Someone also mentioned that you can convert the F40 into the F40 Competezione... They need to finished this feature, and then open the door to the great LM's of the past like the NSX LM, the GTR LM, The FTO LM, etc