Maybe I'm alone here, but I feel like pay per article is going to discourage readership. It now takes the one time decision (aka signing up for the subscription) and makes it into a decision that happens every time you open the site.

There's also a breakeven point with metromile (Google Fi, etc) and a standard subscription. If I recall correctly, they are targeting people who don't drive very frequently, which isn't what I'd imagine publications would want to do.