DICE has announced today that Battlefield 4 PS3 stats will be transferable to your PS4 profiles. Your premium subscriptions can also be moved from PS3 to PS4 when it launches.
However, these transfers are one-time and one-way only, meaning you can switch back and forth with them. Once you decide to move your stats and membership to the PS4, it’ll remain there forever, and you can’t switch back.
Battlefield 4 launches this October for PS3. A PS4 version will follow suit soon after.