I am less intrigued by end prices than the market dynamics at work. Supply is the critical and limiting factor as many unique images are off the market for years, if not decades. I agree with Rhys that one of main forthcoming sources of images will be major collectors who at some point decide to liquidate their holdings. The churn factor is strong and even more recognizable than with cards as most prints have easily recognizable traits that make them easy to trace through the AHs.
I also agree that the sports photos market is unlike any other photography market, and much of that is the result of the gravitational pull of the sports card market. That pull is permanent and evident in the premium given to card images. A sign that the sports photo market is maturing will be when the premium for card images is not so pronounced.
Interesting conservation thread. If you are interested in the rise of baseball photography and discussions of many of the issues in this thread you may be interested in my book.
https://chapmandeadballcollection.com/