Finally here as well. 3 weeks.
The new immersive mode works fabulously in Moon+ Reader Pro. I love that the 3 Android buttons, even after they pop up, are transparent!
They really couldn't be any less intrusive. I also love that, unlike the official KitKat instruction says, you do
not need to swipe from top of screen to reveal the 3 buttons. I'd find that very inconvenient. Although you
can also do that, simply tapping at the very buttom of the Moon+ screen reveals the 3 buttons, too -- that's just perfect!
So, for example, to return to home screen, all you need is to
double-tap the bottom of your screen.
However, all is not well in KitKat for me. My favourite Business Calendar widget stopped working in weekly view.
Worst of all: the display of italic fonts no longer works properly in Moon+ Pro under KitKat. All words in italic appear inside e-books in an ugly sans-serif default font, not in the font you actually activated in your theme.
Say, the whole book is in Calluna, a serif font, but all italic words are inserted in an ugly, plain, sans-serif default font. I wrote to the Moon+ developer to report the bug.