Morkl, great!
So far I've been concentrating on Content Manager - making sure that there is a complete FB2 support. I also touched Home Page - but only slightly. Your work definitely covers it
FB2 support is pretty much done now, starting with build 3.0.55-7 CoolReader properly supports the device (last reading time and standby screen) and
porkupan is looking at FB2Reader.
I was going to continue with Content Manager - expanding the way collections are working. Something along the way of
collection manager for previous Sony readers - only inside the device. Main idea is to have a set of "automatic" collections (in addition to manually created ones) with collection names derived from the names of directories where books are located. This has been working great for years on old Sony devices and allows one to forgo Calibre or Reader PC in almost all of the cases. In order to properly support this I will have to touch EbookSetting a bit - expanding set of available settings.
By no means I am planning to produce anything which is not compatible with the way current software works, so (at least in theory) we would be fully compatible
Are you planning to publish your code somewhere or you prefer to keep it closed?
Almost forgot to ask: what's wrong with fonts in the stock reader?