Twitter could do two things to generate profit immediately: (1) create two clients, one paid with special features, one free with basic features; and (2) run a paid relay. They would undoubtedly have a large part of the user base at least using their relay because of the network effect. They could also build several micro apps, multiple relays for different purposes, etc. They can even do the zap splits that were introduced in Damus so they get a zap of equal or lesser size for every zap made on their client. Another possibility is paid custom algorithms.