Can I suggest something ?
Why don't you keep Pagebuilder Backend (PB3) as an active product for those who prefer that - and introduce Pagebuilder Frontend (PB4) to those who feel for that type of product?
This way you'll attract both target groups ( instead of chasing one away) and thus you get the opportunity to spread the good news of PB4 "internally" amongst your PB3 customers, to convert them in their own pace, instead of having to aquire new ones (which everybody knows is far more expensive).
That will make the user-transition "voluntary" - instead of "forced".
Just a thought...
Have a nice one :)
John.
