A Witcher HD collection (or should that be THD?) of the first 2 games would seem a pretty viable option for some point in the PS4's lifespan.
The Xbox One as well for that matter, since it's not backwards compatible.
Then it would be a question of if the 3rd game could be patched to accept those saves.
Mind you, this is all hypothetical if they haven't even confirmed that Xbox 360 > Xbox One save exports will 100% happen.