Yeah - across 84 existing B737-800s and -700s (ignoring the new delivery B737-Max8s) that $1.3M per aircraft for 6 more Y seats on each aircraft adds up to an extra 504 Y seats in total. Hence, each one of those seats costs VA $218,253, now spread that across 5 sectors per day average, and say 350 operational days per year for the aircraft, and thats 882,000 available Y seat sectors for sale, so then the maths becomes how often do these last 6 Y seats get occupied? Hence, it becomes a "how many sectors hit that mythical 97% or better load factor?" question. Lets say only peak season and peak time flights (footy season peak golden triangle weekday and school holidays bali bogan runs) hit that mythical 97% load factor so maybe 25% of all possible sectors flown across the entire year will have those 6 extra seats per aircraft come into play, so that 882,00 available seat sectors are now down to say 220,000 sectors, so thats 220,000 opportunities per year to stick a paying customer in those additionally created seats so divided by the $110M capital cost, each one of those extra seat opportunities needs to collect $500 revenue (in the case where they are occupied) to carry their capital cost.
Part of the maths will also be the loss of ancillary revenue from loss of Economy X (and people sure aren't going to pay the asking price for the upfront standard preferred seating at the front of the Y cabin).
Two sets of 3 Y seats might weigh an extra 90Kg so they are hauling around an extra 90Kg of aluminum frames and seat cushions every single sector and rarely filling them, but maybe offset by the say 90Kg of weight saved by removing the hard barrier between J class and the Y cabin.
Seems pretty marginal to me but it must tick a $ASK metric somewhere in Bain's head office?