So I go back to the days before open "loyalty programs". So what do I mean?. My father-in-law worked as a high level exec in the 60's and 70's with Goldman Sachs and when he flew AA, he had an AA lounge that existed for the customers AA wanted to treat well. There was no program to join, no membership card to present. AA knew who he was and when he was flying.
There were no miles being distributed or sold unlike today.
However, if you think about the traveling public back then, they paid for a ticket, were transported to their destination, and received absolutely nothing else (except better service and food but for a price).

Now, I buy a ticket and they give me miles (as long as I am in their program.). I use their CC and they give me miles. If I used some no-name credit card, I wouldn't get anything from the airline. So anything I get from the airline is actually a bonus. The bonus may have value if I use it, or it may be worthless since I may fly that airline only once a year. Like Green Stamps, I could give airline miles away or just not use them.
But to say that they are worth less today than yesterday is fatuous. They were given to you as a bonus and your choice is to use them or not. If you use them, their current value is what the airline determines today, not when you were given them, just as Green Stamps determined how many stamps a toaster cost (and that was dynamic pricing as well )

So, are FF programs going away. Not likely unless you get a Bernie Sanders type running the airline (not being political here, just using a well known name to point out an economic philosophy).