I can’t hear a difference in my 1s and SLs, I don’t play them loud though.
 The SL has very different internals than the 1 so it may well be more future-proof than the 1. It will also pair with all of the other Ones which the 1 won’t.
 I really like the real buttons on my Play 1s compared to the touch stuff on the SLs. 
 Sonos does all they can to keep older gear working so I wouldn’t worry about the 1s going unsupported for at least ten years.
                
     
                                    
            There is a good thread here:
 Sonos One vs. PLAY:1 reference
 The difference between a Sonos One and a Sonos One SL is just no mics, and no button to turn off said mics. 
                
     
                                    
            There’s also a good thread here:
 https://en.community.sonos.com/what-to-get-228989/sonos-speaker-comparison-charts-6821929
 Note that both of these threads are pinned at the top of this area of the forum. 
                
     
                                    
            thanks to you both for very helpful guidance