They talk about packaged food and (refined) oil being a store of energy and then in the next breath talk about gold, jumping from a store of energy to an energy proxy without pointing it out or acknowledging it.

Proof-of-Stake might hit all the checkboxes for a currency (fungible, not easily counterfeited, etc.) but misses one of the big features that Bitcoin was trying for, namely decentralization. But I agree, a more in depth discussion would be nice, clearly delineating assumptions and providing going into more detail about each aspect.

I'm no expert, so take it with a grain of salt, but if Proof-of-Work were to have some other incentive built in, like solving protein folding, doing a hard math problem that people care about, etc., this provides an extra incentive structure for the PoW mechanism to be potentially subverted. I'm not sure there's a definitive answer one way or the other, as it looks like there are a few alternatives that do use this idea (see here), but this SO answer gets at why there might be some conflict. In short, tying the PoW to another problem makes them dependent, and if the other problem ever got more profitable, that might provide an incentive to undercut the currency PoW. These problems might surmountable, as I see some discussion here and here but as a simple decoupling, making sure PoW's value is entirely focused on maintaining the blockchain/currency simplifies things, from a risk of attack point of view.