Actually, the real draw to me is that sidechains are an approach to NOT changing Bitcoin.  One of the whole points is that in Bitcoin's current and fairly simple and well-proven form it can backstop an infinite number of customized sidechains but be isolated from problems or failures of any one of them.  Every new functional addition to Bitcoin introduces new possibilities for attack.  Freezing it as a workable system as soon as possible is, to me, a very good thing to do.  My computation of value of each BTC is a function where security and robustness against attack is the dominant variable.

A side-effect of this isolation is that each side-currency is a black box to Bitcoin.  In order to track users, an attacker would have to maintain visibility into the workings of any sidechains that he/she participated in.  Since the focus of some sidechains would likely be privacy and/or security this would make an impossible approach even more impossible.  I expect significant efforts to thwart the development of sidechains for this reason.  At the end of the day, however, the cat is out of the bag and some sort of subordinate chain ecosystem will develop eventually.  As a BTC hodler, I'd hope it would be sidechains using Bitcoin as it's backing store.