By customers, I assume you mean listeners. They only help you survive if advertisers are willing to spend money to reach them.Again, it seems like the industry is more concerned about the advertisers than the customers a radio station needs to survive.
What happens when classic alternative is doing the same schtick in 10-20 years when Gen X'ers pass away? You really think anyone younger is gonna be listening to a format like that to help with advertising?
Radio stations survive on ad dollars, not numbers of listeners that aren’t part of a salable demo, no matter how large the numbers are.
You can’t future-proof a radio format. You go for what will make you money the soonest and has some likelihood of legs. Ten years is great, and the core of a successful demo today will still be salable then.
Twenty? Nope. Your current 35-year-old is 55 and the 35s then are only 15 now. You’ll need a different radio station for them at that time, assuming radio is still a relevant entertainment medium for them—-and that will be more driven by technology over the next 20 years than by available formats on radio today.