* Adds a performance penalty over straight Mapbox-GL.
* No support for animations / flyovers / etc.
* You have to give width/height in pixels for map size.
* Can't introspect map to get layer / point data w/o hacks.
These issues were big enough that I just recently removed this library on a new project in favor of straightforward Mapbox GL JS. The inability to use percentages for height/width is a major drawback. No sense in adding size to the bundle for fewer options.
I was going to comment to say ability to pause/rewind would be awesome. Seems like you've already done that! I also like the interaction of selecting the text you want to speed-read.
One thing that might be interesting, is a shortcut to jump to the article where the current word is.
This happens when I want to glance at a paragraph above, and don't want to rewind all the way back.