I certainly remember the Honda 3 wheeler. I was driving a MGB and a Honda 450 CL motorcycle at the time and had very little interest in this "toy". I thought of it as a backyard toy for kids.
I worked in a little factory as a college student that was "developing" a 6 wheeled amphibious "all terrain vehicle" for hunters. It was suppose to be the cat's meow for duck hunters and the like. It started out with a 12 hp 4 stroke Tecumseh engine which was not good. It had a "dual path" transmission with the input shaft and two output shafts. It was operated with two "sticks" like a skid steer. The business owner fitted a 2 stroke snowmobile engine to the machine and it was completely transformed. It was then fun to operate and rather smoky. Just like now, power sells!
This was 1971. I think the Swamp Fox
was an early ATV, although likely not the first ATV in the market. Here is a URL of a couple pictures of the Swamp Fox. I don't think very many were made. This is my entry into the ATV industry history database!
Swamp Fox. - Amphibious ATV Pictures
Funny how I did not have any interest in ATVs at all back then, but now I do. Maybe now that I'm retired I see the ATV as a "way out" as Polaris used to say.