Seven years... That's my opinion. Product should be fully functional and operational for seven years. That's my opinion.
But I'm not supreme ruler of the world, esp the audio/CE world, so Let's say five years is realistic.
There are original Play 5's, Connects and Connect Amps that will be "stale" at four years.
Weather or not systems work beyond the sunset date, and putting aside any "overreaction" we and our customers are experiencing... Sonos just sent a gigantic red flag up the flagpole... Customers will be leary of spending money on their gear.
I'm Not an engineer, but I play one on TV. My handle is Tweety but I have nothing to do with the organization of similar name. I just had a really big head as a child so folks called me tweety bird.