This would make it easier for PS to charge $499. Take PS4, but with even better specs at it's launch and full BC, knowing people will sell their PS4 to afford a PS5.
PS4's flew off the shelves with just decent specs, no BC, and paid online as a new addition, for $399. PS5 will have full BC and paid online will be the norm. $499 will not be seen as a problem by the majority of early adopters, especially if PS Plus offers a much cheaper bare bones online option by then.