Never on 04 July 2015
Personally, as long as the console supports full backwards compatibility, I wouldn't mind updating regularly because I can afford it and I don't have many consoles to replace.
I replace other more expensive items like my phone and laptop far more frequently than consoles not to, mention collecting other expensive items, such as guitars, so it wouldn't be an issue.
It's more a matter of whether companies can get the install base they need and if others would be willing to upgrade every four years or so. Having game that automatically adjust to the different spec hardware in different gen consoles could fix that. So, for excample, a game plays on an old ps4 but plays in 4k at 60fps with some enhanced graphical features on a new ps5.
