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:
We will not be able to offer you the full or all the specific possibilities of the Miis stored in StreetPass Mii Plaza within this fiscal year, but we can say that you will never let your 300 Miis stored in your Nintendo 3DS go to waste, as we are preparing for a number of software titles, which will feature such as a theme, to be launched in this and the next fiscal years. Nintendo 3DS is hardware designed so that a number of your surrounding people’s Miis in your StreetPass Mii Plaza will generate a synergistic effect on the software to be offered in the future.
Nintendo created a runaway software success on DS with the Mii-using Tomodachi Collection, so a 3D sequel certainly isn't out of the question. Perhaps there will be some functionality linked with the Wii U since Mii characters on both platforms will be the same as each other?