In my opinion, the two major threats to our hobby of muscle cars / kit cars / reproductions / restorations-rods is:
the state governments (who can make it real hard to get your car registered (noise, polution controls, lighting, provenance of major parts, ground clearance, etc)
the auto insurance companies (who can limit our use or raise our rates, or totally refuse to cover our cars). This is the industry's reaction to bad experiences (losses).
I think that good high-octane fuel availability may some day be an issue as well?
This is a gloomy subject. Sorry for being so serious.