I think the big thing Nintendo needs to prove is that the system's got legs. A strong Nintendo launch is not unusual. Keeping it up for another year would be. If they can pull it off, then we may be looking at a new dynamic in the market where they may have a shot at a strong second.
For Sony, they have both the blessing and curse that PS2 is still so damn strong, while Gamecube and Xbox are dead and buried. At least next year post-holiday Sony will be on the PS3 bandwagon instead of the PS2 one with everyone else. Price is definitely a concern, though, and I'd put the magic number at $400.
If Sony sells 30 million units, it's a failure. If the other two sell 30 million units, it's a success, or at least not a failure.
I have the same issue with Sony winning. If they can get away with shoving Blu-ray down our throats, and they probably will, what will they try next time? I wouldn't want to see Nintendo win either because they'll just retard technological growth. I'd be okay with Microsoft winning, not that I see it happening.
5 months in, and despite all the hype, we still do not have an announcement that Wii is getting an exclusive the likes of Resident Evil for Gamecube, and I don't expect to either. This time around, it's not even that easy to do ports for Nintendo. You can only move so many systems based on Nintendo's games alone, as we've seen in the past. They need to convince third parties the system is not a joke and to bring out major games like FF, GTA, and MGS (if they do, they need to then help with the marketing so that these games actually sell instead of getting lost like all the other third party games on Nintendo systems), and at the very least they need to get back to the days before they lost all their second party developers.