Hello @thellimist. This is some stuff i could find on sidechains.
Videos:
Whiteboard presentation sidechains
Articles:
Sidechains: Why These Researchers Think They Solved a Key Piece of the Puzzle
Hacker noon article: what are sidechains
Papers:
Original sidechains paper 2014
Non-Interactive Proofs of Proofs of Work 2017
Sidechains Presentation slides
Chimeric Ledgers: Translating and Unifying UTXO-based and Account-based Cryptocurrencies 2018
Discussions:
If anyone knows of more resources let me know and i will add them to the list. 
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