There is no need for people to come here poo-pooing the mere idea that someone would want to do this.
@
Dark-Show,
I would seriously think about utilizing calibre's conversion, and possibly, recipes, infrastructure.
Again, there isn't a lot of open-source -->AZW3 conversion code around, and calibre is most of that, so why not reuse it? Otherwise, it should serve as documentation for re-implementing your own conversion code.

Also see our Wiki:
MOBI or
KindleUnpack
calibre's News recipes are pretty popular with some people -- I don't know how many would rather use your hack vs. calibre, but there is probably some call for on-device usage.
calibre's recipes are also an easy way to get well-written support for many websites out-of-the-box. You could fallback on some sort of generic screen-scraping for anything else.
It's not reasonable to ask people to install third-party ARM builds of all of calibre

but some kind of stripped-down lightweight alternative would definitely be interesting.
calibre is all GPLv3.
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shamanNS,
Two words. "configuration file"
Thank you for your concern.