Could T2 usb ports be upgraded from usb2 to usb3 ?

Why would you think that it is? USB3 is upgraded hardware, not just a driver. It requires extra conductors.
But USB3 devices can generally be used with USB2 ports
- but you may have known that already...
Are you just interested for increased performance, or was there some other motivation to the question?
It would be a totally pointless exercise. USB2 is plenty fast enough to record two HD streams in real time. My Panasonic TV will record two HD channels using a usb2 port. The limitation is the pvr itself. not the data port speed.