This is a bit of a moot point, as far as Apple is concerned.
"[...] It is completely backward compatible with DisplayPort v1.1a and requires no new cables or other equipment [...]" - Bill Lempesis, VESA Executive Director.
A 1.2 device will work as a 1.1a device.
The features that you'll loose out on:
* Driving displays in excess of 2560 x 1600 x 30 bpp @ 60 Hz (Apple LED Cinema Display tops out at 2560 x 1440 currently).
* Multiple display daisy chaining (LED Cinema Displays only have a single Mini DisplayPort jack and as such cannot be daisy chained).
* AUX channel data transport at 720 Mbps (beaten by the PCIe transport layer rates within Thunderbolt, which when driving a LED Cinema Display at full resolution leave about ~2Gbps available for data).
* 3d stereoscopic display support (Aww, no Avatar 3D).
* Additional audio format support (mostly related to Blu-ray, which Macs still don't do).
It's sad, yes - but there's not much incentive for Apple (not sure about Intel) to support 1.2 currently. And since Apple is going to have exclusive use of the Thunderbolt interface until it starts showing up on other PCs in 2012, Intel only really has to meet Apple's requirements while they finish up the rest of the spec (optical cabling, etc).
Maybe they'll find time to add in 1.2 support by then.
Wasn't the original idea of light peak to be optical? Why didn't they deliver on that promise, I want my future back, it's frickin 2011 now and we still don't use optical connectors to connect our devices :)
(I guess they'll have a hard time with the 'Thunderbolt' icon when they go to optical, it makes even less sense for optical than for a low-voltage connector)