They sort have already, and it did not kill the sport. I remember you had to pay for the finale of ****nal's 'invincible' season.
Interesting way of looking at it and for most of Hearn's shows i'd say you're right. What I meant though is that with it being so low on the list of priorities and Sky not willing to spend their overall budget on it, without PPV how do the big big fights* get made? I suspect they don't. *In no way do I consider the likes of Joshua v Whyte and Bellew v Ceverly "big big fights" though.
I would be surprised if it's PPV unless its included as part of an event similar or Rule Britannia or Repeat or Revenge. Although I'm not a bean counter, a complete O2 sell out and a standard fight night budget should be ample for all parties involved. If they start paying big additional purses to bring in overseas World Champions or include higher profile Matchroom fighters then yes it most likely would be a PPV event.