There are a lot of photographers who are not aware of metal prints. I have a local client who I see daily and is becoming very popular in the underwater photography category and at his shows, he receives a lot of attention because his metal prints stand out so much compared to everyone else who mostly have frames canvas/paper prints.
Each artist is different and each art subject is different as well. My home is Mediterranean themed so a metal print just would not match and would look out of place.
My metal photo lab is right next door to a very popular marine artist who has his work licensed by several major companies and clothing brands. he loves the metal prints but he simply can not offer it because his style is canvas, hand painted and a metal print just doesnt work for him.
With that said, Metal Prints are here to stay. They are more for the contemporary/modern home and people who want something unique. besides being cool and unique, they are also practical since they dont require a frame. If I were to say a particular medium is fading, I would say its the acrylic prints being pushed out by metal prints.