I did learn on GameShowNetworkNews that the median age is now 50 as opposed to 65 a few years back, and is skewing younger demographics.
If anything happens to pre-1990s material, the least that might happen is the demise of Match Game on GSN. No wonder it airs at 5:00 a.m. in the Pacific, when a lot of people are probably still in bed. There is speculation from someone on said blog that the lease to air The $25,000 Pyramid might expire later in May. Should be very interesting to find out what's in store for the surviving classics fans in the coming weeks or months.
The only programs I can see replacing pre-1990s material someday are Woolery's Lingo, Whammy! and Deal or No Deal. We might get Louie's Feud, but that is just speculation.