I struggle to see how it makes money. The legacy carriers won’t want everyone to have a lie flat seat, when that’s the main driver of J class revenue. I can’t see it tempting the likes of FR or Norwegian, whose business model is based on selling tickets as cheaply as possible.
Essentially, you’d be looking for an airline who want to pitch themselves as an all premium economy experience. VS is probably the best fit of existing airlines for that. But even then, given that Premium Economy is supposedly the most profitable of cabins on planes, you’d think that if that market segment could profitably support more seats, they’d be there already.