Compared to other remasters, the GM's was quite bland. Same with the original D-series remaster until it got a part 2. And the D-series got a 2nd remaster soon after the original. It's been 3 years since the original GM remaster, and I'm sure that more people want it. Edit: looking over it, the D-series got it's remaster almost exactly 1 year later, it's just now going on 3 years since the Grand Marshal remaster.
At this point the Grand Marshal badly needs a remaster, it just doesn't fit in with other cars, it has lack of customization and not too many configs compared to the D-Series.