Yes, it is possible to hack a Mac through the new DisplayPort/Thunderbolt interface, exactly the same way it is possible to hack Macs and PCs through FireWire interfaces.
How? Well, as Thunderbolt expands the PCIe bus, buying a Firewire to Thunderbolt adapter will suffice. This is the same approach as many pentesters, myself included, have used when encountering laptops without a FireWire port on pentests. Simply using PCMCIA or ExpressCards to expand the bus and add a FireWire port will do the trick. I finally got the hardware to test this out last week, and it works like a charm. Plug n’ Play FTW.