I hesitated to post this message, but I really wanted to thank your for what you have done : Plato is much faster than nickel and better looking than KOReader, it is almost perfect!
Here are a few drawbacks and issues is noticed/I miss from the other reader.
- you can add a book to a collection with an empty name. That should not be possible I think, because it makes the collection hard to click on

actually I think a collection name should contain at least one character.
- the table of contents is nice, but it would be even nicer to have a button to close it without selecting an entry
- large table of contents are hard to navigate through with swipes. Will you consider adding a page number to the TOC, which you can click on to directly go to a specific page?
- and, although that is much more difficult to integrate, I do miss a dictionary and the annotation features from Nickel (and I must say that annotation is slow and hard to use in Nickel). Perhaps dictionaries could be used as a separate app (like sketch and calculator) if it is easier. Or instead, you could add a button which toggles between PageTurn mode or Annotation mode. In this mode, long pressing a word would show it in the dictionary or highlight it like in nickel.
EDIT : That question has already been asked a lot, I am sorry

And it was written in the doc/TODO.md in the github page. my bad
I may have missed some of these features, in this case I apologise

Anyway, these features are not easy to implement, I know, but I am only suggesting, not asking for them

do as you wish, you already gave us a lot with this app as it is!