new buildings

This is unlikely to happen due to the quint being a ranked reward, if you are bellow the rank required you must pay 25 coins, the vehicles you get with the stations are technically free and this would be away round the rank requirement, because even if you make the station with a quint purchasable with coins it would only be 25 coins which would be less than the 30 coins it costs to build a station. The quint is a great thing in its current form as it gives the player something to work towards and if they don't want to it gives them an option to skip the work.

Another reason is the quint costs 19K each when you reach the rank requirement where as the Type 1/2 are only 5K each so it would be a lot less to buy it with a station.