First, there's these cranes on the outer part of NLA. They'd provide a good view of the city, and its most striking landmark, the BLADE Tower is in clear view.
Next up, my personal favourite, the floating islands near Tallon Rock, which provide an even better view of the full city, as well as some more of Primordia itself. The edge of Tallon Rock would admittedly be a bit in the way, but I imagine for a Smash stage, that could be moved out of the way.
Then I got the two big floating islands over in Oblivia - I'm not really sure which one of them would be best suited, so I took pictures of the view from both of them, as well as pictures of the islands themselves.
For Sylvalum, I also got two possible locations: First, the peak just north of the eastern part of Lake Ciel, and second, one of these huge bow things that are all over the place, with a good view of the lake.
Then, for Cauldros, one of these floating mining stations would probably be best suited, so I went with one just off the west coast of the continent.
And lastly, for Noctilum. . . I admittedly didn't have much of an idea. Anything near the Divine Roost would be cool, but there's not structure in-game that would really work for that, unless they moved these gigantic branches and leaves over there. Instead, I simply went with the wooden pathways around the middle path of the continent.