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Yeah and I posit that @gmaxwell is going to be the spectator.
Side-chains are fundamentally flawed and can't ever work securely. Lightning Networks can't work decentralized.
Side chains are constrained by a fixed number of coins. As far as I can see, without an emission of new coins there is no practical way to secure them with one notable exception; namely
demurrage. The credit for this belongs to Freicoin
http://freico.in/I know this is controversial but it can work, particularly for a side chain whose purpose is transactions as opposed to wealth storage. A 1% per year demurrage rate is not a real issue if the velocity of money is say 2 weeks.
The problem is incentivizing mining, because merge mining is insecure, side-chains can't create coins, and transaction fees are not incentives compatible in PoW.
How do you envision demurrage incentivizing sufficient mining to secure a PoW side-chain?
Secondly merge-mining suffers from 50+% attacks if the chain being merge-mined doesnt have a majority of total hashing power... which kinda defeats the point if we're worried about miner scalability.