Nintendo, for whatever reason, seems allergic to HDDs. Nintendo is more likely to use SSD if anything because they're Nintendo and doing something sideways and ass-back-upwards (you read that right) is typically how they do things, especially since HDD for saving games in consoles was kind of Microsoft's idea. Nintendo is just too proud to admit another company may have had a good idea. SSDs are more expensive, but the benefits seem more in line with Nintendo, namely durability, smaller form factor, and less frequent failure rate among others. And it happens to have a faster start up. I would want 128 GB, but I would expect 32 GB or 64 GB which compared to the HDDs in PS3 and 360 is nothing. Still, it's leagues better than what the Wii offers.
What I think will happen is that the wii 2 wil be about the same dimensions as the 360 slim. Nintendo will include the option of HDD storage in their next system and then play it off like it has never been done before(not in the open), but the consumer will have to supply their own hard drive for the system.
I also see them allowing all forms of memory storage to be implemented. This would include both SD cards and external stoarge devices such as flash drives and USB HDD. But like I said, you will have to provide the medium for the console. They will do this to avoid hearing consumers bitch about storage options.
As for online features, cloud storage might be a little too advanced for Nintendo's tastes, but I do see them having online that is similar to either Home or XBLA. They will provide a basic plan, but they might charge 2000 points per year for a more advanced version of their online option.
As for multimedia, Nintendo will most like;y include a music player, but the true cream of the crop will be a movie player. What is most likely going to happen is that Netflix will get its own preinstalled channel and all you do is set up your account and instant streaming of HD movies is at your finger tips.
This might be trivial, but I would like to see an accessory be released with the system that plugs into a Gamecube controller port or USB port that allows all virtual console games to be played with their respective controller. I have discussed this before many times and I can not argue enough for it to happen.
The wii 2 will not try to out perform the 360 or PS3, but it will be to those consoles what the 3DS will be the PSP.