I do think it would be smart for Nintendo to focus their game development efforts on a single hardware architecture and software/services platform. Most people seem to imagine that taking the form of a single handheld device with some kind of TV connectivity – but I think it would be fine, and preferable in some ways, for it to remain separate pieces of hardware.
Have two devices, one a handheld with a single lower-end smartphone-grade touchscreen, and the other a small TV console + controller, sharing the same smartphone/tablet-grade hardware, same basic OS, same dev environment. (Maybe give the console a bit more horsepower – an extra CPU core, a bigger GPU – for higher-resolution output.) Have them both support the same games, all digital, with cross-buy, and saves and whatnot synced through a common account and services. Price them each at ~$200.
Execute on that plan well, and I think that could be a decent way for them to continue to have their own little ecosystem. The ship has probably sailed for the foreseeable future on competing directly with MS and Sony, or having a major 3rd-party ecosystem – so if they want to continue having their own platform, they need to consolidate and maximize their ability to support it alone.