The only art that OP showed that isn't SE's own property are the concept art for the background but SE already has concept art for Mt Gagazet from base to summit. All other work OP linked was taken directly from FFX concept art or FFX in-game screenshots/renders.

I'm frankly kind of surprised at the number of people saying that Square can't utilize anything the OP posted because "legal reasons". I know knowledge of the Final Fantasy franchise isn't needed to play FFXIV but nobody commenting seems to have even googled anything (or read my previous comments) regarding this topic. There's no argument nor reason why this can't be added into the game aside from "will it make sense in XIV's story?" in the same vein as how we got Rabanastre, Kefka, Exdeath, Cloud of Darkness (twice) and Chaos.