From a practical view vs enthusiast.
(1) wait to see what Price SB notebooks are, if reasonable and within budget - go for it.
(2) From what you have indicated, a good core-2-dual will work. (not withstanding some future requirement.
(3) advantages of SB:
a - Much better igp, But playing a DVD seems to be the current preformance requirement. You indicated DVD playback - A T6400 will play a Blu-ray just as good as an i3, or SB laptop.
b Usb3 and sata III support. sata III will not help a mechanical HDD. However; it will benefit the Newest SSDs that are SATA 6 - But you could upgrade to a SATA 2 SSD cheaper, but still small (requires only SATA II included w/I3). So SATA III will only help if you Upgrade to SSD that is SATA 6 - bear in mind small size say 120 Gig and probably approx $250 upgrade where as a Sata II SSD will become cheaper and still blow the doors off a Mechanical HDD. USB3 support is a big advantage - BUT that depends on how offten he will use a thumbdrive, and in his case a USB2 (High performance) Thumbdrive would be fine.
Bottom Line a I3/I5 laptop would be great, But I would wait to see the cost differnetial.