What has history taught us?
For a year or more leading up to the 5d3 this question was the dead horse that it seemed like everybody took a whack at, of course regarding whether or not to pull the trigger on a 5d2.
5d3 comes out and you can basically get two 5d2s (Holiday season 2011 prices $1899 new) for the price of a 5d3. Had we all known that the price difference would have been so dramatic a lot of people would have had their xmas family portraits taken on a 5d2 instead of a xxxD or been out shooting with their 5d2s instead of on the forum seeking advice.
There is no question the 5d3 is a great camera and satisfies a lot of what the 5d2 leaves to be desired. But if you bought a 5d2 that price difference just doesnt make you feel bad about your decision.
Will we see history repeat itself?
The main features we all like to see improvements on are and this is taking all types of photography into consideration: Resolution, Speed (fps), ISO performance, Dynamic Range, Auto Focus, weather-sealing.
Sure there are a ton of other things but, if there is a marked improvement, in any of those features that I mentioned above, over the current 7D then you may feel like you made a bad decision to buy a 7D now. I'm not going to say that I don't think the new 7D will be a vastly improved because I definitely didn't see 61pt AF coming on the 5d3, but I also didn't see that price either. So if we are surprised with by how great a 7D replacement spec list looks, get ready to be shocked by the price. So, with all that said, buying a 7D especially if you are able to get it at a bargain will not be a bad move, and I don't see you regretting it.
The only point in waiting until after photokina would be to hope for another price drop on the 7D. I've seen it as low as $1349 USD body only, its at $1449 right now. If it gets any cheaper I'll be buying one myself.
But obviously if money is no object go buy a 1DX and be done with it!