OneGo is an interesting idea that introduces the ability to set up flight subscriptions on a monthly basis. They claim to be the first booking app for subscription-based flying on major airlines.
The way it works is you select a flight plan, regional or national for unlimited flights to anywhere within the US. They claim that soon you will be able to make unlimited changes to your trips and reserve up to 8 flights in advance. Check our their nationwide and regional options. You can still maintain your frequent flyer miles as normal but note that OneGo is apparently currently only offering economy class seats.
OneGo was set to launch last month although I’m not certain if that has become a reality yet. Learn more here from their FAQ section.