Soundwave on 30 October 2018
Regarding the Wii U attach ratio it's higher because attach ratios rise as a system gets older people, use some common sense. A person who owns a system for 3-4 years is going to have more games for it than someone who owns a system for 6-12 months most likely. As Switch gets older, its attach ratio will rise, the software sales on the Switch are very strong, way past the 3DS or Wii U at equivalent time points.
Hardware wise its trending basically right on par with the PS4. The challenge as I've said for Nintendo is going to be getting high sales in the later years of its life cycle, but that should be doable with a Pro revision.
