i wonder. I don't *believe* HDMI cables are "intelligent" though i could be wrong (ie I don't think theres a chip of any kind built into them) so although the spec has changed in some way the devices at either end won't know what spec of cable they've got attached. It might be that a 1.4 spec cable will work fine - personally i'd at least give it a go.
Spoke to Chord directly today and yes they have confirmed that 3D WILL pass through the 1.3 HDMI cable although they do have a new 1.4 cable coming out as well!
We used Chord HDMI Active cables for our 3D dems at the Bristol Show, and they worked fine. I guess the new Chord 1.4 cable will be different in that it will have the extra wires required for Ethernet connection between components, which is part of the 1.4 specification.