The numbers are public record, the entire market can be studied by looking at ammo sales. The most popular ammo goes into the most commonly encountered gun chambered for the ammo. When Remington took over Marlin and company they also bought some proprietary chamberings. Those will most likely continue as long as sales are there. As for new offerings, I would say we'll most likely have to wait for this next election cycle to see much change. The .45-70, 30/30, and pistol chamberings are most likely to stay.
Just my guess