Não há garantia de que isso aconteça, já que a nova tarifa baixa, Basic Economy, é explícita que, por preço, você abre mão de algumas opções que outras tarifas mais caras têm, incluindo a seleção de assentos.
A transportadora atribuirá assentos desocupados e não pedirá a outros passageiros que se movimentem para acomodar aqueles que viajam juntos.
Entre as outras restrições de tarifas, clientes da United adverte (ênfase adicionada minha):
We're introducing a new fare option, called Basic Economy, which is available on select routes and in addition to standard United Economy® fares. Created for our customers who may be more price-sensitive, these lower-priced fares provide most of the same inflight services and amenities that are available with standard Economy — such as food and beverages, United Wi-FiSM and inflight entertainment — but with some important restrictions that you'll want to be sure to review carefully before booking:
Seat selection and upgrades are not available
When you choose a Basic Economy ticket, your seat will be automatically assigned prior to boarding, and you won't be able to change your seat once it's been assigned. You will not be eligible to purchase Economy Plus® seating or receive Economy Plus subscription benefits. MileagePlus members, including Premier® members, cannot use complimentary, earned or mileage upgrades.
Group and family seating is not available
Please note that customers traveling in a group, including families, will not be able to sit together.