This theory sound kinda convaluted and stupid but hey I thought it sounds like a good idea to throw out there.
As for Mickey's involvment, this has me confused. Because Nomura said the secret ending takes place in the past but you could think of it as teh future or something to that extent. My initial reaction was Mickey shows up before he received his Inverted Kingdom Key (I.K.K. for short). But then I thought what if the scene with Mickey was in the future, and somehow he lost his I.K.K.^ (either another keyblader was chosen or he no longer needed it due to peace being restored and he could no longer summon because the keyblade wasn't needed.
Then I thought to myself again what if Mickey's involvment in the new secret ending was in the past. Maybe Mickey originally had the Star Seeker since he was Yensid's apprentice, and this place where the battle was fought was actually the realm of darkness, which was transformed after the UEM unleashed kingdom hearts. We don't know how large teh realm of darkness is, only that it has a beach and the sky's look similar (at least to me they do when you see Mickey). Since Mickey's I.K.K. is the representive of the Realm of Darkness it came to him because he had the strongest heart in that area. So that could explain how Mickey got his I.K.K. though I have no clue what would've happened to Star Seeker, maybe it went back to Yensid I dunno. It's just an idea to throw out there too.
As for Mickey's involvment, this has me confused. Because Nomura said the secret ending takes place in the past but you could think of it as teh future or something to that extent. My initial reaction was Mickey shows up before he received his Inverted Kingdom Key (I.K.K. for short). But then I thought what if the scene with Mickey was in the future, and somehow he lost his I.K.K.^ (either another keyblader was chosen or he no longer needed it due to peace being restored and he could no longer summon because the keyblade wasn't needed.
Then I thought to myself again what if Mickey's involvment in the new secret ending was in the past. Maybe Mickey originally had the Star Seeker since he was Yensid's apprentice, and this place where the battle was fought was actually the realm of darkness, which was transformed after the UEM unleashed kingdom hearts. We don't know how large teh realm of darkness is, only that it has a beach and the sky's look similar (at least to me they do when you see Mickey). Since Mickey's I.K.K. is the representive of the Realm of Darkness it came to him because he had the strongest heart in that area. So that could explain how Mickey got his I.K.K. though I have no clue what would've happened to Star Seeker, maybe it went back to Yensid I dunno. It's just an idea to throw out there too.