Yup, this is still the question.
Maximizing time near VO2max is commonly referred to as optimal for eliciting improvements to VO2max, but the correlation is far from fully mechanistically established.
Here’s one reference chain back to 1986.
(Read this review first, if any. For a comprehensive review of HIIT training methodology & physiology)
I’m not satisfied with this conclusion though. There are very possible mechanistic pathways downstream from systemic VO2 that may be more related to cell signalling & adaptations (which I don’t know enough about to speculate too far just yet).
Whatever the case, most likely improving your own VO2max will require improving your specific limiter to VO2max. That might be peripheral somewhere in the muscle fibers, or central cardiovascular structure/hemodynamics. Traditionally it’s thought most athletes are central (O2 delivery) limited, hence the empirical relationship btwn time near-VO2max and improvements to VO2max.
All that being said, I don’t think work-matched intervals scattered within a longer ride would be better than the same intervals done sequentially. But maybe if the scattered intervals allowed you to go harder and/or longer, ie. higher total work vs iso-effort (same RPE) intervals done sequentially?