I can understand people's concern, but I suppose I'm viewing ARR as not just another numbered FF, but almost a celebration of FF itself. We've got Magitek and materia woven into the game's lore, which were staples of other games, but they did it to where it worked. I know these aren't characters, but I don't see it as much different than Lightning showing up. We've also got nice charms like the Goobue mounts, the Warrior of Light helm, the Onion Helm, and I'm sure we'll have other items that show up that nod at other entries in the series.
While I know actual items, mounts, etc. aren't really part of the grand scheme, how are Magitek and materia being part of this game's lore much different than a character (which will probably not have any lore that affects the main story, in my opinion) being brought in. Correct me if I'm wrong, but I don't recall Magitek or materia being in any of the other main entries.