Best answer by upstatemike
Probably better sound but how much better? For some use cases the difference might not be enough to matter so we will have to wait until October 31st to quantify the value of this.
Can be paired for stereo - Major Advantage!
Can be linked to a subwoofer - Major Advantage!
Can play music from local library - Major Advantage!
Airplay2 - Niche Advantage.
Supports many more music services - Niche Advantage (most people only use 1 or 2)
Good integration with Connected Home systems (as long as you use DLNA and steer clear of the new API)
Syncs with other Sonos devices.
Third party hard button remotes available
Syncs with other Echos using permanent named groups
Bluetooth Out - Niche Advantage - for Bluetooth headphones or speakers
Bluetooth In - Niche Advantage
Can be used as a speakerphone - Niche Advantage that may become major - can call other Echos (intercom), call any outside phone number, and can accept incoming calls or dial 911 on your land line ($40 adapter required.)
Built-in smart home hub - Niche Advantage
Line Out Jack - Niche advantage for headphones or to link to larger stereo, etc.
Available hard button remote that also acts to extend voice command range - Major Advantage