I don't think Ford have underestimated Mustang, I remember they were talking about 2000 units per year which is what they're moving. The problem is the delay to get them here.

Apart form initial flurry they need to forecast to sustainable volume. I'd say depending on price 1-200 GT350's might have been possible but they're only building a few 1000 a year in the US and that equates to not worth it based on needing to RHD it for our consumption ratio..