This reminds me of Markerly (http://www.markerly.com/).
There's a large potential to layer additional meta data and ways for readers to engage but I haven't been a fan of existing solutions, especially for mobile readers.
I may try this on my blog. I like the idea of people being able to interact in different ways, although I really don't know how many people really hover over text like that in articles and expect something to happen.
Reminds me a bit of Tynt (which was acquired by 33Across). They focused on tracking what people copy & paste and share (via email). They were tracking a huge amount of data, but I don't think they could monetize it well enough.
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