But sidechains, they will not survive - better technology is already here.
What is this technology?
OT is one such technology, that dosn't need to change the Bitcoin protocol, so no risk of of Side Chains altering the incentives in mining Bitcoin over time.
I'm a huge supporter of OT, but I'm not sure it's a replacement for sidechains. The two technologies do different things and have different goals. I look at OT as the liability system to Bitcoins asset system, and sidechains are still assets pegged to the original bitcoin without needing any third party to do the peg. OT is best for pegging tokens to other things, like precious metals or shares of a company, with a third party doing the peg. Even if pegging to bitcoin using a distributed pool, you still need to trust the third party group of cosigners that control that pool.
Side Chains (SC) offer some of the same features, but with SC there is the possibility to do it all on the Bitcoin protocol, one can uses Merge Mining to secure and process transactions without an entity controlling it.
The big difference is SC alow you to secure BTC, and mover the value onto another blockchain, this changes the dynamic that motivates miners to mine Bitcoin.
If a miner can mine a SC and earn, he could abandon Bitcoin mining or mine empty Bitcoin blocks worse 51% attack Bitcoin, without sacrificing her mining income. The scenario is far fetched but just the possibility puts me off.
A more likely scenario is SC-tokens backed by Bitcoin get exchanged for other SC-tokens, and a SC that stores Bitcoin but isn't as secure as Bitcoin is attacked or exploited, cutting of the return path for the BTC, thus permanently removing value from the Bitcoin blockchain.
If there were a failure or loss of some Bitcoin it would be a Bitcoin failure, unlike Gox there won't be anyone to blame.
None of this is a concern while Bitcoin's block reward is high, or SC are implemented in centralized entities, but just the fact that a for profit company is proposing a protocol change that makes possible the option to separate BTC the currently form the value stored on the blockchain is a red flag.
The biggest advantage I see is decentralized exchange and we don't need to change Bitcoin to alow SC for that.