Does anyone know if there will be new islands similar to the Sevii Islands in Emerald? I heard that you can catch Mew and Celebi there

there are simalar islands. but they all have different legendaries on them. world edges island contains mew. naval rock contains lugia :wub: and ho-oh. southern island contains the other lati depending on which one you chose. birth island contains deoxys. mirage island is just lucky to find, you dont need any special tickets like all of the others.
mirage island has wynaut ranging from lv5 to lv50. it also contains the only leichi berry in the game.

thats all of the islands. hope i helped