How do I disable PM notification?

[Darkrad]

Hello, recently after discovering some disturbing bugs related to it and with MyAlerts in presence, not seeing any particular good point of it, I am thinking of disable PM notification feature on subscripted threads entirely. 

Changes should effect:

• Users shouldn't be able to select PM Notification for their default subscriptions setting.
  
• Users shouldn't be able to select PM Notification for their specific subscriptions.
  
• Users who already subscribed to any thread with PM Notification setting should get those resetted.