With NOS, this is simply law of supply and demand. There is a finite supply and continuing depletion of that finite supply over time. There will come a day when NOS will cease to exist, I can't predict the day. I assume the larger stashes from closed down factories and hoarding individuals are fast disappearing. Pre-boomers and boomers both had access to large stashes at cheap prices, these guys dead or dying off, where will these stashes come from in future? At some point, end of nos will bring about price pressures on new tubes unless manufacturing ramped up.
Hopefully we'll see both innovations in tube manufacturing which will create new tubes with improved quality over nos, and increased production capability. If not, the future may become grim at some point. As for myself, I mostly now use unusual tubes not in high demand or have my own stash of both NOS and more common tubes.
