you hit it square on the button.
one can argue boundary effects all day long but in the real world, for how many potential owners, even enthusiasts, is this going to be the #1
for the vast majority, any potential theoretical advantage of the one are going to be far outweighed by practical issues of cost, installation problems/concerns & room layout/decor as well as sound quality.
besides, while the cancellation effect of near boundaries effects all frequencies, its greatest impact on room modes is bass. and
unless one is willing to spend the money for a closed back design plus stuff a whole lot
of insulation in the space or build a containment box (if that's even possible), there will be resonances & sound transference issues with in-ceiling speakers. advantage offset by disadvantage.
And, as he himself pointed out, the internal Dolby crossover for the overheads is about 180 Hz, so I'm not sure how relevant the issue even is. probably not much.
his ongoing speaker debates are very similar to the one he raged over home Atmos to begin with. I'm also at a loss to understand it...in every Atmos thread it's the same poster with the same outcome.