Similar to how it was done with ICC, I don’t see why all raids progressively get easier after say the first month. This would help curb people just all out quitting the game because the content is too difficult for them.
So for month one, dungeons are their normal difficulty (cater to the harcode fans). After that first month damage done increases by 5% a week or something. After a few weeks the increased modifiers are enough to all even pugs to clear the content (now catering to the casual fans).
This allows both hard core and casuals to enjoy the content and would help overall slow the mass exodus we see from raiders and general players alike.