Good news, sort of.
iOS 11.2.5
Lyrics can still be displayed. The new, undocumented, convoluted and unnecessary method is as follows:
- Tap on the Now Playing banner to bring up the full Now Playing screen
- Tap on the artist name - album title (shown in the Now Playing screen). The display will return to the menu the song came from
- Tap-and-hold the song to bring up the pop-up menu
- Scroll down and select Lyrics from the list
You can also read the lyrics for a song even when it's not playing, by tap-and-holding the song title in any menu and selecting Lyrics from the pop-up menu.
This discovery is thanks to user idafromhammel.