We've been doing the Alexa based whole house audio for the last 8 months, and it's gotten better and better. In the beginning, it was just one echo connected to a whole-house amp - but since, we've added more, and more speaker grouping. Places like the Master Bath that doesn't have speakers can be grouped with the Master Bedroom, or the Whole House echo and play in sync. I also use the Announcements to tell the kids what I want them to do, like come up for dinner, or STHU even. Most recently, Ring started working nicely with it - so a doorbell press announces through every Alexa device in the house that someone is at the door. Hell, lately even our thermostats have Alexa - so you can walk down the hall and say Alexa, play children's lullaby on Daughter's room if I hear her struggling to get it (she's 4 - nobody understand her, not even Alexa).
Soon I'll expand it - I have the Monoprice zone amp which I'll combine with a 6-zone, 12 channel amp to bridge multiple zones together... but for that to work really well, I need to get some automation happening so I can override and put it into certain modes when I want, then have it reset itself back to my defaults later - like putting each channel on a separate input and putting the volume back up... that way my announcements continue to work as expected...
My single biggest complaint is that, the only way you can use different spotify accounts on different Echo devices is by having the Echo devices on different Amazon accounts - which breaks announcements, drop-in, doorbell, grouping, etc. So - I'm working to move off the family Spotify account and moving to Amazon music, which is truly inferior. Spotify with Alexa is an awesome experience if you don't need different family members to be able to listen to different streams at the same time.