What is the difference, either conceptually or practically, between a side chain and a separate currency? And pegging two chains price-wise is equally pointless because then it basically *is* one currency.
It seems the BTC crowd want to experiment with innovation without 'harming' their sacred cow, but they can't have it both ways - you throw your ideas to the wolves and if it survives the wolves you have a winner. Tying the wolves up and slapping muzzles on them first doesn't help the evolution of your idea, it hinders it and you learn nothing of value from the experiment.
Plus, it will take years for any of this to happen anyway, if it ever does.