Hopefully free but I would guess if anything this might be a reason for a version 6 at the worst when it comes to charging. At least that would seem to be a fair outcome especially if other features are already lined up for a 6. £20 for the upgrade plus other improvements wouldn't be a bad worse case scenario but as Wittaj says, free would be better.
As for it's implementation, if it can be done on a an NVR with limited processing power, it can certainly be done on a PC. As I see it, it's nothing more than a script setting up an additional stream from that camera and telling the software to apply a fixed digital zoom centred on the tracked object.