Higher density sounds like it refers to the all-Y discount vacation airline they're talking about. Presumably they want to copy the "Comfort Class" model of charging extra for nicer seats without having to have a separate flight crew or catering or airport experience.

It sounds like there will be J/Y planes for business destinations and Y+/Y planes for vacation destinations, not just 2-3 destinations each year but all the smaller destinations that aren't London, Paris, and Frankfurt.