when you factor in the overlap of people who purchase both a handheld & home console each generation and now only need to buy a single device than yes 80 million is a good number.
regardless i dont consider something a success based solely on hardware numbers things like software sales & profit have to be taken into account as well. if Nintendo sells 80 million units of Switch over the course of 5-6 years, sells a few hundred million units of 1st party software, a few hundred million units of 3rd party software and makes the company a few billion dollars in profit than yes it would undeniably be a success.
Let's just consider that SW sales and profits are proportional to HW sales. 80M is what Nintendo made last gen while crying in agony. How's that going to be a success this gen?
Don't take me wrong. I believe (because NS can overlap clients from 2 shrinking markets) that 80M is ok. But to call it a success? No way.
Prediction made in 14/01/2014 for 31/12/2020: PS4: 100M XOne: 70M WiiU: 25M
Prediction made in 01/04/2016 for 31/12/2020: PS4: 100M XOne: 50M WiiU: 18M
Prediction made in 15/04/2017 for 31/12/2020: PS4: 90M XOne: 40M WiiU: 15M Switch: 20M
Prediction made in 24/03/2018 for 31/12/2020: PS4: 110M XOne: 50M WiiU: 14M Switch: 65M