Possibly impractical feature request for the Reader: I would love to be able to choose line width/line height as well as font size. When I'm staring at Chinese onscreen for protracted periods of time, as I do on a pretty regular basis, my eyes eventually get tired and I start losing my place much more easily. Increasing line height and decreasing line width has been a pretty effective way of dealing with this for me, and it'd be great if Pleco could do something similar.
On the blue-sky, I-want-a-pony side of things, it would also be neat if Reader had a mode like Spritz and other focused-reading apps, though presumably this would require some pretty heavy-duty automatic sentence parsing. Displaying one character at a time wouldn't work; one word at a time might be okay; larger chunks of text would probably be better, but figuring out where to start and end them would be a massive pain.
(It would also be super-sweet if we could opt for columnar RTL text, but I'm not sure how useful anyone other than me would find it, and I'm sure it would an absolute bear to code, so maybe wait for Pleco 8.88 on this one.)