My predictions:
1. Nintendo will release a harddrive that will allow for updated character rosters, move rosters, and possibly voice chat. Adding and/or removing of characters, and moves will be based on polls in the Everybody Votes channel, you will only be allowed to vote if you have an SSB save on your Wii. This will be the first of many games to use the Everybody Votes channel in this way, but it will also be used to change other things in this game and others, like new options, new menus, and many other things upgradeable through the expanded harddrive. Don't expect SSD or flash as Nintendo is looking to offer a lot of room for a little bit of money. Keep your finges crossed that they ask if random battles should be ranked!
2. Online only modes, one of which will include Mii Battle which will to allow you to choose your favorite characters moves (won't be affected by Everybody Votes channel unless you personally update it) and load them into your Mii. While using Kirby's moves your Mii will take on one physical trait along with the move set of your opponent when swallowed and digested. Online only modes will also include mini-games like who can hit the sandbag more in 30 seconds, and a whack-a-mole type of game using Super Smash moves.
3. Certain unlockables will only be available through online play all will require friend code battles since random matches are not counted.
4. Tounaments will be hosted by Nintendo. No word on how often this will occur but expect rewards ala Pokemon rares at live tournaments, could just be unlockables spoken of above. Host friend codes will either be included in manual and/or posted on Nintendo.com.