...
For the record, I never touched any alts other than Namecoin and Litecoin. Namecoin was never about value, and I only dabbled in Litecoin like a hedge more than anything else, although I had little doubt that ASICs would make their way to SCRYPT as quickly as they made their way to Bitcoin (this was before ASICs, and I had no idea they would make it to either near as quickly as they did). That having been said, as I have previously stated, when the idea of sidechains came about, it was so that non-Bitcoin functions could take advantage of the biggest most secure blockchain without bloating it with non-Bitcoin information. To that end, I am not against sidechains, and would even say it would have made sense for Namecoin to be a sidechain if it were going to catch on and actually compete with our centralized domain name registry. However, I have yet to see obvious any arguments that adding complication and storing Bitcoin information outside of the Bitcoin blockchain will actually solve any legitimate problems.
For the record, I never touched Namecoin or Litecoin because I was to lazy. Both of these I thought of as 'good' things and created for basically the right reasons. Probably...I was to lazy to research them fully.
Namecoin in particular was of high value and I would dearly love to see it implemented on a sidechain. Going off on a bit of a tangent, yesterday my power was out and when it came back on, every http/https web page was being intercepted on both of my computers and sending me to a page which said that my 'mydish' account was suspended. I don't and never did have an account with Dish Networks, and my system (Exede) does not even use the same satellites. This was happening on both my unix box set to use Google's resolvers and my windows box which gets the resolvers via DHCP. This means that either my router or modem was hijackable, or that Exede's abilities to intercept and modify traffic was compromised. It actually was not a DNS issue because nslookup worked and going http://{ip} also resulted in a redirect to mydish.com. The issue cleared up while I was on the phone with tech support and they agreed that it was very bizarre and they claim they had never heard of it. Anyway, it's scary stuff to those with a basic understanding of traffic shaping and it should be a warning to those who feel that there is no way we'll ever see problems of excessive control down here on the consumer side of the Internet...even in 'free democratic' countries.
Lastly (and back closer to topic), I would point out that to Bitcoin a sidechain should look much like any old user. It is no more 'storing Bitcoin information outside of the Bitcoin blockchain' than it would be keeping one's private keys private. To the extent that it is, that is a good thing in my mind. There is utterly no need to document your purchase of a hamburger in a persistent (forever) way which is replicated on multiple copies of the blockchain and distributed around the world. Cool as it may be, it costs money and limits flexibility. It is also something of a privacy issue to be honest.