I can say that I am on pace for a 500,000 point/mile year with only 4 cards so far:
Citi AA 75k
Amex business gold 75k
Chase marriott 50k
Citi Thankyou premier 50k
By the time you go through a cycle of all the cards that are not churnable, the banks come out with something new and the cycle begins again.
Having a side business is very helpful to open up all the business card opportunities as well.