Almost every operating system has a tts-voice assistant. Although we have screen reader, its not like Cortana where you could say “Hey Cortana” and then it will listen.
However, using a Gnome Shell extension, it might be a good idea to think about having this. For example,
Person: “Hey Ubuntu, play KIIS FM on odio (snap package)”
Ubuntu: “Now playing 102.7 KIIS FM (L.A.'s #1 Hit Music Station) on iHeartRadio on odio.”
Thats just one example. But, it’s something that would take a year to develop, so now is a time to think if we want one by Ubuntu 20.04 assuming we will still use gnome shell.
It’s current quality for users (compared to existing proprietary competitors)
The success/failure of previous voice-recognition projects. (example)
You’ll quickly see why this idea seems unlikely to get much traction for '20.
Remember that Ubuntu’s focus is on distributing upstream software. If you find some good upstreams that could be packaged for Debian and Ubuntu (or snappified for Ubuntu), please do let everyone know.
Alternately, if you discover a simple integration problem preventing several otherwise-compatible upstreams from working together to provide this functionality, do whistle.