Ah right, quads won't draw on Unity UI in Unity versions older than 2017.1, since it'd cause a nasty crash before that, sorry about that!
There's no event to subscribe to yet, I think only the index of the current letter being read out is exposed. The value could be exposed, but it would just be an integer of the current line. Another way this could work is that... STM puts a line break character (\n) at the end of each row, so that could potentially be used, too? I'm trying to think of the most user-friendly way to fix this...
Working on other fixes now!