Drive chains could have some utility for privacy, but I think the anonymity set would be too low. Paul acts like people would replace their Monero with Monero-on-Bitcoin. There is ZERO chance of that. Ditto for any other existing coin. BCH on Bitcoin? I don't think so. Ethereum? LOL. 

Drive chains would be additional revenue for miners, where they are given control over a new shitcoin circus. Maybe that's fine-- but it doesn't scale Bitcoin. 

Maybe Paul is right that not everyone needs unilateral exit, but no one is going to use a chain that miners can just "take away". Miners won't have rugging powers, but they will have extortion powers. 

I'm (very cautiously) optimistic about Ark, Spiderchain, and some covenants. I think an ideal solution would be built utilizing lightning. It's possible scaling won't be achieved for another 15 years, that doesn't mean in the meantime we should enable fuckery that would be difficult to undo.