Putting it very mildly. The hub spoke model required to fill these fatties might not be dying, but it is certainly decaying. And even if full loads could be achieved, it would still fail to leverage an economy of scales effect as it has a higher CASM than several smaller models. Add to that the exorbitant development costs vs the low sales numers, and you got yourself one gigantic mess. The only feasible use case is for slot constrained airports, but since it requires special treatment like dedicated gates and super category wake turbulence spacing, it cannot even shine in that area.
As a pax I love it, but for airlines it is almost always an inferior choice. As long as pax aren't willing to pay a markup equivalent to the CASM difference, there is basically no business case for it.