I think the difficulty would be when choosing which factory to build a model in.
It would be a nightmare to a new player who might choose an existing factory and not realise it is already being used to manufacture several other models - maybe they just got the sliders balanced the way they wanted on the existing model only to have production fall off a cliff and demand spike for that model when the new one muscles in on productivity, or else to only realise when the new car enters production that they have to put that new car’s production to zero (having spent a lot of money and waited a long time for it to enter production).
Because of this time difference, a huge amount of gameplay might be lost if they choose to go back to a previous save. I will sometimes design 5 or 6 totally new models in the time it takes for the first design to be engineered and enter production.
You can always use your imagination and name your factories A, B, C of the same city or something and think of them as being on the same complex.