For a company that builds their brand loyalty on keeping existing customers happy with their purchases (via OTA updates and slow replacement frequency), 4.5 years isn't long enough in my opinion—hopefully there weren't a ton of play:5 buyers in that final year. Forever isn't reasonable either of course with how heavily cloud based they are. I think it should be closer to 10.
It's a little hard to imagine 2010 devices keeping up in 2020, but I'm sure that 2030 will be kinder to 2020 hardware. In the same way a 1995 laptop is far less capable than a 2005 compared to 2015. I think they could make that commitment.
I give Sonos a longer time I would others because they justify their price tag based on how unlikely you are to have to replace it. Rather—that's how I justified all of mine.
And they should be up front with what that duration will be when you buy it.