Ok, I'll put it in this way... There are several scenarios regarding availability, IQ and price of 5d3:
No matter whether you buy or not there are following events possible:
A) Soon there is 5d3...
i) which is not much better for your needs than 5d2...
ii) which is much better than 5d2....
1) and costs much more than 5d2
2) and costs comparable to 5d2
B) 5d3 is soon announced but available in a few months...
i) which is not much better for your needs than 5d2...
ii) which is much better than 5d2....
1) and will cost much more than 5d2
2) and will cost comparable to 5d2
C) 5d3 is not so soon at all
i) which is not much better for your needs than 5d2...
ii) which is much better than 5d2....
1) and will cost much more than 5d2
2) and will cost comparable to 5d2
So as far as it's for fun only, we could spread some percentage probability on it.
A) Soon there is 5d3... 25%
B) 5d3 is soon announced but available in a few months. 50%
C) 5d3 is not so soon at all 25%
and
i) which is not much better for your needs than 5d2... 25%
ii) which is much better than 5d2.... 75%
And
1) and will cost much more than 5d2. 75%
2) and will cost comparable to 5d2 25%
So finally these events (as dependent) have the following probability of occurance
A) Soon there is 5d3...
i) which is not much better for your needs than 5d2... 6%
ii) which is much better than 5d2....
1) and costs much more than 5d2 14%
2) and costs comparable to 5d2 5%
B) 5d3 is soon announced but available in a few months...
i) which is not much better for your needs than 5d2... 13%
ii) which is much better than 5d2....
1) and will cost much more than 5d2 28%
2) and will cost comparable to 5d2 9%
C) 5d3 is not so soon at all
i) which is not much better for your needs than 5d2... 6%
ii) which is much better than 5d2....
1) and will cost much more than 5d2 14%
2) and will cost comparable to 5d2 5%
I assume that:
- if we'll have case C) then you'll be happy with buying now (you have fun with new gear regardless IQ and price of 5d3)
- you care about money (if you don't - you always can buy now 5d2 and sell it later loosing several bucks)
finally please pay attention, that you'll regret buying in cases:
A)ii)2) - better model soon at good price
B)ii)2) - better model later but with a good price
So there are 14% chances you will regret buying NOW and 86% you will not regret. Therefore it is around 6:1 for now...
I am also sure a lot of people here would show you that it's rather worth to wait and also would be right.
What else can say... I was in the same place as you some time ago and do not regret my decision

Please treat it as fun anyway - I had some free time and good mood so could play with unpredictable probablities

. Anyway - nobody but people from Canon could answer your question truthfully

