Michal hey, that's an interesting take at it 🙂
The extension in question installs and works, because since I haven't got any reply, I have re-written it to use static content scripts (defined in the manifest) instead of dynamic content scripts (defined programmatically).
I didn't re-check it now, but if you didn't implement it so far, missing chrome.scripting.registerContentScripts API will cause all extensions using dynamic content scripts to install, but not work, because their content scripts won't be executed.
If you seriously aim for supporting Chrome extensions, you should consider implementing this API among the first ones to be implemented 🙂