Nintendo Won't Keep Miis Cooped Up in the Plaza

More 3DS software coming
Seeing all those Mii characters shuffling about in the 3DS Mii Plaza with little to do might be a little disheartening to watch, which is why impending first-party software that will utilise players' Miis will be good news for many.
At the financial results briefing for the first quarter of this fiscal year, an investor noted that they had almost 300 Miis "stored like captives" in their StreetPass Mii Plaza with little to do, and asked Nintendo president Satoru Iwata whether the company had any plans to release software that will make use of these Mii characters and be able to form some sort of connection with other users. Iwata replied:

As we hear that a fairly good number of people have already done everything we offered with StreetPass Mii Plaza, we are preparing for something new that you can enjoy there in the near future. We are planning to make it available by the end of this calendar year.

Nintendo will bring a number of software titles to 3DS users that will utilise accumulated Miis, and using these Miis as a theme, future software will be able to establish a level of synergy with the StreetPass Mii Plaza: