Just read "What's next" from CR: a funny sentence is - "One of them will NOT be the 5D3"... Logic and wish tells me the rest.
There are many reasons to wait at least until Nov 3rd -
1. Patience is important feature of character
2. A chance to read more about techniques and experiences of other people and with other devices (not only Canon) and compare.
3. Save money, more money
4. Much better peace of mind is to buy when no one expects further announcements in the year.
You misread it. The November 3rd announcement is rumored to have 2 cameras... one of them will be a professional camera will the other one will NOT be a 5D3. Everyone just needs to stop taking everything as a signal to the 5D3, the 5D3 will not be until next year around this time.
If I recall correctly, the 5D was released about roughly one year after the 1DsII and the 5DII roughly one year after the 1DsIII. If past performance is anything to go by, Canon could take up to a year to announce the 5DII's successor. After that, you need to factor in a delay for RAW conversion software to become available if you do not use DPP. You also need to consider whether you really need to buy the camera directly after release - for the initial period after release, expect to pay more (closer to RRP) for the camera. With time RRP and street prices will drop. Since the 5DII was released, the price of the body has dropped by close to $1500 in Australia.
Canon may however announce a 5DII successor sooner after announcing the 1D X, for reasons such as:
- Competitive pressure - Nikon has caught up in terms of "affordable full frame"
- next year being the 25th anniversary of the EOS system
- split in the 5D line.
I am not budgeting for a 5DII replacement until at least a year from now, unless my wife has a need for a second full frame body before then.