Well, I hope they upgrade the controller at least. Not to say I don't like the Cube controller, but there are a few things that could use fixing. The 'Z' button either needs to be scrapped or a guide to using it needs to be included in development kits or something. The pressure sensitive triggers have too much lenience between them not being used and them clicking in. It's a minor thing, bit it can be annoying when a game requites one of them to be pressed all the way down to perform a vital action (such as Metroid Prime or Time Splitters 2). The last thing, they should make two sizes of the controllers. Most of the people I know generally like the GC controller, but those with big hands find it uncomfortable to use.
I would suspect the memory cards will need to be a lot bigger; a few third parties this generation find memory storage a little too hard to handle, it will be much worse the next one.
I really don't understand backwards compatibility games-wise too well. If people own GC games, presumably they will own a GC; so if people who own the N5 also own GC games, then they would own a GC as well. The only people I would see this benefiting is people who will try to flick off their second hand GCs when they have no need for them, flood the market and hoard the games, which are no longer in production. Then second hand GC game prices would soar. However, Nintendo doesnâ€™t care about this market at all, the only advantage they could possibly obtain from such a move is if they still manufacture GC games for all the people who just bought old GCs or a new N5 to buy. That would cannibalize software sales for the later console, which is something Sony is willing to do, but Nintendo is much more focused on software.