[Superman]

There is a substantial capital investment to get tooled up. But the process is not especially dirty. Tubes are made of metal and glass, and sometimes a plastic or fiber base.

I'd like to think there will always be a market for tubes. Some of us think computers just cannot make an amp do what a tube can. Musicians will love them until they die, and further generations will do the same. Some musicians just insist that tubes bring a truly unique dimension. This musician sees it that way. There is no substitute. All of my professional music gear, and all of my hifi gear, is 100% tube (preamp and power section) with one exception. I have a bass head that has two vacuum tubes in the preamp and a toroidal transformer in the rear. Class D.

But I think in the long long run, tube gear will continue to dwindle. It sees a resurgence from time to time, but tubes were mostly replaced by transistors many decades ago.