Lucario - his time has come and gone. He was a popular and unique character, however some of the newer generations need to be represented this time around. My guess is that they will replace him with the newer version of Mewtwo who will share some similar moves. There isn't enough time and Lucario isn't a high enough priority.
Ike - will be replaced by a more recent Fire Emblem swordsman. They will also be heavy and share somewhat the same moveset. Not enough time to keep him in and add another Fire Emblem rep.
Snake - very unique character, unfortunately does not represent Nintendo in any way. Will be replaced with another third party member. Think he was just put into Brawl to make people happy.
Wolf - it'll be a shame to see this guy go because we are losing a villain. But Wolf is way too similar to Fox and Falco, and it's too much to have 3 representatives of the same game have similar moves.
Zero Suit Samus - this one I am really not too sure about. But I just don't see her returning
Pokemon Trainer - Squirtle and Charizard are more iconic than any of the newer starters in any generation so it will be sad to see them go. But I can see them getting replaced by the same 3 Pokemon combo but from a different generation.
R.O.B. - even though it is such a unique character, I feel it won't make the cut.
Lucas - I'm not sure if he will be cut or replaced with a newer Earthbound character, but I don't see him returning.
Toon Link - he adds the quicker, alternative version to the heavier Link. Many have preferred the quicker version since Young Link. I can only see him staying in because of the re-release of Wind Waker and if they incorporate those weapons into his arsenal. Like the Wind Waker, Deku Leaf and Grappling Hook.
Ike - will be replaced by a more recent Fire Emblem swordsman. They will also be heavy and share somewhat the same moveset. Not enough time to keep him in and add another Fire Emblem rep.
Snake - very unique character, unfortunately does not represent Nintendo in any way. Will be replaced with another third party member. Think he was just put into Brawl to make people happy.
Wolf - it'll be a shame to see this guy go because we are losing a villain. But Wolf is way too similar to Fox and Falco, and it's too much to have 3 representatives of the same game have similar moves.
Zero Suit Samus - this one I am really not too sure about. But I just don't see her returning
Pokemon Trainer - Squirtle and Charizard are more iconic than any of the newer starters in any generation so it will be sad to see them go. But I can see them getting replaced by the same 3 Pokemon combo but from a different generation.
R.O.B. - even though it is such a unique character, I feel it won't make the cut.
Lucas - I'm not sure if he will be cut or replaced with a newer Earthbound character, but I don't see him returning.
Toon Link - he adds the quicker, alternative version to the heavier Link. Many have preferred the quicker version since Young Link. I can only see him staying in because of the re-release of Wind Waker and if they incorporate those weapons into his arsenal. Like the Wind Waker, Deku Leaf and Grappling Hook.