It'll enable point to point flights for many airport pairs which IMHO is the future of air travel. Connecting flight are too slow, too unreliable and too expensive to run.
Low cost airlines will use it to eat the more established players' lunch in longer haul flights (cross country, international).
So far no airline has managed to crack the low-cost transatlantic nut, usually they try it and collapse in a few years. I don't think anything is significantly changing in that regard.
LCCs thrive on extremely efficient utilization; they basically match planes and crews to maximize as much time as possible in the air for everybody and as little rest as legally allowed. This is easy to do if you are a short haul carrier with lots of short flights that could reasonably slot around.
Transatlantic flights are 6+ hours. This makes things more difficult in terms of scheduling, particularly since these LCCs will probably only have a short-haul network to use up the rest of the time on one side of the pond. The longer a crew is in the air, the longer their required rest period is, and that decreases utilization.
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Most of the money on transoceanic journeys is also premium journeys (e.g. first and business.) It's how British Airways books $1B in revenue annually on JFK-LHR alone. But LCCs don't really target this group of people, and the budget-conscious are a fickle market for such long journeys. They also can't easily attract this more expensive customer unless they stump up the cash to provide equivalent amenities, but then that blurs the line between legacy and low cost carrier.
Low cost airlines will use it to eat the more established players' lunch in longer haul flights (cross country, international).