I would be seriously disapointed if this were so, just because I hate Xemnas and thought he was a dull antagonist, but anyway, that's not the basis for my conclusion that MF is not Xemnas.
Yes, the swords are similar. They aren't the same however. Not only are they a different color, the designs on them are different. They are different weapons.
blue lighting only came out of MF's hands for like, a second while he was summoning his weapons. I really don't think he actually uses blue lightning. Even so, just because two people use blue lightning does not mean they are the same person.
do they really have the same body? I think not. We can't really say anything about MF's body except for that he is wearing a black coat, and that isn't very significant because Riku, Mickey, AtW, Xion, and all members of the orginization also use the same coat.
This is pretty insignificant tbh, anybody can use weird symbols :/
He also uses the doom spell (used by Marluxia), and he uses Meteor (a command exclusive to Terra), and he uses Tornado (an attack exclusive to Ven), and he uses Renewal Barrier (a command exclusive to aqua) and he uses megaflare (an attack used by the TAV trio), and he uses several attacks that Vanitas uses.
So we can't determine his identity based on one of his attacks.
There are a couple similarities, but I'm afraid we can't draw conclusions based on them.