"Big business"??? Yes, in the specialist car industry, in the real car industry? Not even a blip on the map.
GM going after Mongoose, etc. is not due to Superformance. Understand that the Grand Sport license is held by Duntov Motors and Superformance is just the manufacturing/distribution sub license holder. In other words Duntov is the entity that holds the license with GM and Superformance is the "hard parts" supplier.
GM had already, I understand, warned several companies well prior to the Superformance Grand Sport announcement. GM as well as Ford, etc. have legal representation who watch the specialty industry looking for trademark/IP infringement. Sure they are looking for royalties and income, but the trademark protection and possible abandonment result is the real driver here.
I hate to see a small company like Mongoose having to defend itself against GM but they knew they were on shakey ground using the name "Grand Sport" on their kits.
I used to hold a license form Ford to maunfacture restoration parts and use Ford trademarks, logos and even had Ford supply the original blueprints to me. My parts had to be inspected for quality and I had to carry product liability insurance that named Ford as additional insured! There are some real horror stories of companies like Ford and GM being sued for products they did not make nor were even aware of because their trademark or IP was on the product. Sort of like you having to pay for your next door neighbors wife's auto accident that you had nothing to do with.....