Best answer by melvimbe
This is also what I would expect logically. Your Kitchen Sonos (or an Sonos zone in your system) is not tied specifically to any particular echo. Therefore, the echo would not know which sonos zone to display.
I think there is a strong possibility this could change in the future, where you specifically link a sonos zone to an echo. There are lots of advantages to this setup, and Amazon currently has similar links between echos and firetv.
However, if/when that functionality is implemented, I doubt song lyrics will be available. Displaying the lyrics requires that the display device and speakers are relatively in sync. Currently, echo 'hands off' the music request to Sonos, it does not stay in sync with Sonos as doing so would be rather cumbersome. So for example, if you paused your music through the Sonos app, your echo would not know that immediately and would continue scrolling the lyrics.
I can see where displaying lyrics would encourage users to play songs from Amazon rather than other music sources, so perhaps they'll figure out a way to make it work.