As always, devs could put it in the game and no one would notice its not made by them. Actually i think people would say "why does the Coupe GM look nicer than other cars in the game?"
Bonus points for maturity over the leaking problem as well. I guess some people thought it was so good, it was worth releasing early
This is amazing! However, I have a bit of a suggestion - since someone below said it looks like a modern moonhawk (and it does), think about how the Crown Victoria, the Grand Marquis, and the Town Car all look the same - Maybe a slight rebadge for a Moonhawk facelift :D? All you'd need are slightly different head/ taillights, different badging, and some new interior parts, and you'd be set!
In terms of this mod, I don't think anything needs to be said. It's a mod by NinetyNine, so it's good. That's just what I've come to expect of you :)
Personally, I have never really liked the in-game Grand Marshal. However, this version, the Coupé, makes me like it a little bit more. This seems to me more of the BeamNG version of the 89-97 Ford Thunderbird and 93-98 Lincoln Mark VIII which also takes some cues from each line's predecessors the 83-88 T-Bird / 85-92 Mark VII. This is a well built mod and so far I have not experienced any mod-specific or irregular issues at all (I've only had this installed for a few hours so far).