Note I'm not advocating a ban as such. I think it would be a shame if all petrol powered vehicles were banned, if only for historical appreciation. They might be banned from or face restrictions on their use on public highways though. However it does seem likely there will be a push back from petrol heads on that.
The air cooled leap in value didn't happen until more than a decade after porsche switched to water cooling when people realized vintage 911s had been undervalued for decades (they are excellent cars, especially with modern tires). There is likely now a bubble, especially with 912s, but there are tons of porsche guys buying both old and new stuff.
I don't see current Harley guys taking to electric very well, but this is about getting a whole new generation of buyers, not about keeping their aging boomers happy.
Porsche enthusiasts also show similar preference for air cooled 70~80s models which appreciates in value....but they kept almost all parts of the formula (the car look, clock, engine in the rear) the same because when they went with a bold new look (like the tear drop of early 2000s) they were facing an uphill battle.
It's sort of like the HN comment I see calling for petrol cars to be banned because electric vehicles are going to render the old ones extinct.
There is a true lack of understanding the market and the buyers in a space that most HN'ers are not the target demographic.