It all depends on how much time and resources Nintendo puts into it. Miis were cool when they debuted because they were new and different to the console world. But as twesterm said, they got old in a hurry. There was the Check Mii Out channel that Nintendo added not long into the Wii's life, but again, after 20 minutes of that, what more was there to do?
Yeah, you could get creative and make some outlandish characters or download amazing replicas of celebrities, anime and video game characters, but maybe about one to five percent of Wii owners did that. There was also the voting channel (can't think of the name off my head), but again, once you asked yourself, "Why am I doing this again?" and realized there was no point, you tucked it away and never thought about it again.
Nintendo could have sent updates to add things like new clothing, hairstyles and other little quirks, or had real awards and incentives for winning Check Mii Out contests or polling questions. But those things never happened, those channels stayed stagnant, and it got old real fast.
If Nintendo wants Miiverse to be relevant, it needs to show users that it will remain fresh, vibrant and updated. We need something different to look forward to constantly. And to begin it all, Nintendo needs to find a way to tell less socially/technologically aware consumers, like grandpas and soccer moms, that it's their in the first place. I can't tell you the number of people I knew that owned a Wii and didn't even know it could go online...
I think Nintendo should have included a 500 points Wiishop card with every unit. It's not much, but it would have sent the message to every owner that there is more to the system than playing Wii sports. It would have raised awareness about the Virtual Console and WiiWare and got more people trying those games out.
But I digressed. To reiterate my point, if Nintendo truly wants Miiverse to be a killer app, it has to push it to the moon instead of hyping it for a short while before dropping like it has done with so many peripherals or features of consoles past. Facebook wouldn't be the omnipresent behemoth of a social network that it is today if the people running it were content to sit on their laurels and play second fiddle to Myspace or remain static after that war was won.
I'm not yet convinced Nintendo has the focus to pull off something as huge as a full-blow social network, but I'd love to be wrong.
