Regarding smaller phones: I'm not sure whether one-handed operation of a large-screen phone is really viable with stock / unrooted firmware, which is what most users have; there are simply too many other areas of Android that make that impossible. So I'm reluctant to throw a whole lot of design effort at making one-handed Pleco viable on a Galaxy Note unless I see evidence that a lot of Galaxy Note users are trying to operate their phones one-handed and are succeeding at it outside of Pleco.
In other words, if Google and Samsung can't be bothered to improve one-handed operation on large-screen phones then I'm not sure if many people will notice or care that we do. (Samsung at least would appear to be actively favoring two-handed use through the S-Pen)
Re your specific items: on 1), how are you managing to operate your device's keyboard if you can't get your thumb all the way across the bottom of the screen?
On 2), I don't see it as obtrusive enough to require a setting to hide it unless we get a TON of complaints (and we haven't on iOS, where it's worked this way since November and where there's considerably less screen real estate available).
On 3), the reason the bar is hide-able when the keyboard is closed is that it's unnecessary (just makes it a bit easier to open input), whereas with the keyboard open it's the only way to switch between input methods; we had an option to hide it with the keyboard open too, one of the many options we removed in 3.1, and again we'll probably only bring it back if we get a lot of requests. Input method switching is tucked away much more unobtrusively
on iOS but the lack of a standardized keyboard on Android makes it challenging for us to do likewise on that.
On 4), aren't tab bars at the top of the screen pretty much universal? How do you navigate between them one-handed in other apps? I'm generally against swiping within screens because I find it confuses our navigation metaphor - left/right suggest hierarchy, pushing into / popping out of a particular screen.
Re intents, we actually support both ways - we fire intents when you create a launcher in Settings/Miscellaneous and set a result when you do a CREATE_SHORTCUT action - but it appears that in some cases OCR might be using the wrong one, so we'll see what we can do about that.