So the objection I hear all the time about this idea is author permission, plagiarism, etc etc.

Here's the rundown:

1. Anyone can excerpt anyone else's work with proper citation.
2. Nobody except the author is reaping any financial reward for the content.
3. Nobody is representing that the content is from anyone but the original author.

So yes, this is entirely legal. No, you don't need permission to excerpt. That's what sharing stuff online (links, retweets, reddit posts, etc) are all about. Yes, links back to the original source are included. Yes, the original author will receive all the money escrowed on his or her behalf.

Could an author still be upset? Well, people can be upset about anything. Do I think it would be reasonable for an author to be upset about free promotion and potential additional payment streams? Not really.