The intercom functionality has always been requested by users, and should definitely help sell more Echo devices to users.
According to Amazon, "millions of customers" have multiple Echo speakers in their homes.
The new Routines are rolling out slowly, so it may take you a few days to see the option within your Alexa app. Conversely, you can use the hot words "Alexa, tell everyone..." or "Alexa, broadcast..." to issue your announcements.
Alexa announcements are rolling out to United States and Canada starting today and will support all the Echo devices Echo, Echo Plus, Echo Dot, and Echo Look. Google added a broadcast feature to its Google Home smart speaker back in November past year, in fact.
It was not immediately clear at press time whether the announcements would also come out of Alexa-enabled devices like Amazon Fire tablets, but it's likely that only smart speakers will work with the feature. This feature was reportedly already available on Amazon's Fire HD tablet.