Video presentation (https://www.youtube.com/watch?v=rNi6ZbMKh_w) | Article form (http://www.nintendo.co.jp/corporate/release/en/2015/150317/index.html) | Summarized version (http://www.nintendolife.com/news/2015/03/guide_everything_we_know_so_far_about_nintendos_deal_with_dena_smart_device_plans_and_more)
In short, Nintendo is coming to mobile devices, but they will not be porting anything. There's also a teased system called the "NX" being worked on.