The limit is not as restrictive as you might think. There's enough cards on offer that you should be able to churn a new card at least every 2 months whilst waiting for other card's exclusion period to expire.
Happy if it works for you, but churning every 2 months isnt very practical for me for a number of reasons:
1. I use cards to book travel - accommodation, short haul LCC flights and you often need to present card to check-in/board; or if relying on CC travel insurance then the card needs to stay open until trip completes. I often book big trip trips 10-11 months out, because of how difficult it is to secure time off from my job.
2. Quite a few recurring expenses and subscriptions, changing CC details every month is a real pain (and maximises chances something wont get paid n time), i just dont have the time to manage all that.
3. If I've paid an annual fee, I want to get max value out of the card so not just the sign-on, I feel its better to keep 11 months and get the ongoing best points earn.
Its easier if you want to do multiple programs, but my primary focus is Qantas as that's who we have to fly with for work (short haul economy) and means i have best change of earning SC. Heaps of points without status means you have less chance of being able to use the points.
I already have Westpac, ANZ and Amex cards - there is really only 4 other semi decent Qantas options NAB (my next visa, but as a fee not til March 19), Citi, Qantas and BankSA/StGeorge/Bank of Melbourne (as SGB group are treated as one) left, and of those only NAB had good ongoing points earn. The CBA cards have insulting earn rate.
If i were to apply for 4 more cards this year, then I'm locked out for 12-18 months (so zero good options next year, and left with not the best earning cards, as the ones I have all earn more points on regular spend than the alternatives) and would have outlaid 4 annual fees for bonus points i wont be able to use this year anyway, so rather save the cash and churn at a slower rate.
I dont think there is a a one size best approach for all scenario. I will have enough points for a J RTW oneworld redemption by July; and dont have the leave to take such a trip until 2019 (as already have 6 weeks personal travel fully paid ffor this year) so i can afford to churn slower.