I think an important correction here is that they say they will only commit to a minimum of 5 years of software updates after they stop selling a particular model.
Even then, there is no reason the speaker wouldn’t still work. To me, that sounds perfectly reasonable. There’s posts about a 15 year old play 5 speaker getting a firmware update within the last year even, so I think Sonos deserves credit where credit is due. They have a proven track record so far, but no doubt it’s something to keep an eye on going forward.