The Blockstream team has made it CLEAR they have NO interest into alternative currencies built on a sidechain. This is absolutely not their vision of sidechain and it is explained repeatedly in the white paper.
Adam Back
sidechains are a generic extension mechanism. we hope many people make use of the sidechain extension mechanism to add innovative new features centered around the bitcoin currency.
from the White Paper Appendix C
Atomic swaps
Once a sidechain is operational, it is possible for users to exchange coins atomically between chains,
without using the peg.
It sounds like altcoins to me.
Yes of course it is possible to create "altcoins" or, commonly referred to in the paper, Issued Assets.
My point is the main innovation they are trying to put forward, if we can trust their writing, is using application specific features of altcoins without having to issue a new currency.
The altcoin approach of creating a new cryptocurrency just to introduce new features creates uncertainty for everyone looking at cryptocurrencies from the outside. There seems to be no natural stopping point, each fork can be forked again, ad infinitum. This creates both market and development fragmentation. We think that for cryptocurrencies to be successful as a whole we must build network effect, not fragmentation.
To accomplish this we propose technology to enable new cryptocurrency networks that do not need new cryptocurrencies
http://www.blockstream.com/2014/10/23/why-we-are-co-founders-of-blockstream/The whole point of this exercise is to leverage Bitcoin's network effect and sound economic foundations while fostering innovation from within.