Interesting that you put para spacing above line spacing. I would not have expected that. I personally really want line spacing (we have it on Android) as many fonts have too tight of default line spacing for my taste. (It is different for each font - and defined by the creator) - which we faithfully render in BFR. On iOS, I now use Asian font sets like Hiragino Mincho to read, as they have much wider line spacing, and support western chars.
I get that para spacing is nice, but curious what you find critical about it.
Do other readers of this forum feel para spacing is the top prio?
Also interesting that you really value the muilti color coded highlighting. On my wish list is to automatically use different colors for when a highlight has a note attached or not, and enable users to choose the two colors. I thought that having multi colors was kind of extraneous - mostly for education, and there are apps specific to that space (e.g. Subtext, VitalSource). Maybe just my own personal proclivities there though. If I may ask, what do you use the different colors for?
As to annotations, our first step is to sync location in book across devices. Then next step is to sync annotations. We do have an "export to email" for annotations/highlights. Do you find the import/export as XML useful or important? if we had annotation sync?
making text selection better will probably have to wait until we put in a new EPUB rendering engine (for EPUB3 ad EPUB2). So I don't expect to "win you back" anytime soon, but I do appreciate the feedback.