Just get it when you need it. Apple laptops retain their value like no other, so feel safe knowing you can resell for a nice chunk of change.
Hell, the cMBP may never be upgraded again for all we know. They could be discontinued once a new rMBP refresh arrives.
I don't know that the rMBP need thunderbolt 2. Apple may have just decided to stagger the releases this year to make it easier on the supply chain.I think they're probably waiting to outfit the new rMBP's with Thunderbolt 2 and the new wi-fi standard. I'd say they'll be out before year's end. Likely around the same time as the Mac Pro.
well, its quite expensive machine, would like to get ac wifi.. if they kill it, that would be sad... i am looking for machine that would substitute my imac.. and air seems to be out of the game, because of display (imac has to go, cause there is no more place for this big guy)