I don't know. But I have been wondering how vintage cards will hold value as the fans of the players on the cards age out of ... life itself. I am interested in the cards and players of my youth. How many non Baby Boomers will desire a Mickey Mantle card, 20 years from now? Essentially what injected money into baseball cards is the Baby Boomers growing up and wanting to spend money on cherished objects of their youth....creating the big boom in cards.
Sometimes I think baseball card collectors want the cards to be "investment grade" more than they actually might be.
I also wonder this a lot lately. In one way, the supply of vintage has gone way up. No, the amount of cards still in existence is actually the same. Very occasionally a lot will be discovered and enter circulation, but this is now a rare event. Everyone knows baseball cards might be worth money, so no one throws them out without checking with someone first, or putting 20,000 junk wax cards on Craigslist for a silly price.
But in the 21st Century, potential customers of cards have access to scores of sellers of most cards, simultaneously, whenever they want. You no longer have to repeatedly visit shops or card shows to find that last '59 high-number you need ... it is now on eBay 24/7/365. This access to supply effectively increases supply, in terms of resulting prices.
I think vintage cards will always be desired objects. There are kids today just getting hooked on Coca-Cola who will want 19th century Coke artifacts when they have money to spend as adults. But how much desire = demand = prices there will be, again, I don't know.