You piqued my interest enough to go hunting - this StackExchange[1] question estimates ~19% of fuel is spent on initial climb-out to 30k feet for a 737-800 on a 5-hour LA->JFK flight.
Without doing hard calculations, it intuitively feels pretty marginal potential flight weight savings for the operational complexity it would add
Without doing hard calculations, it intuitively feels pretty marginal potential flight weight savings for the operational complexity it would add
[1] https://aviation.stackexchange.com/questions/47262/how-much-...