What you will see between now and the end of next year is a new 1D IV and 1Ds IV. I don't see the 5DII being updated next year. But realize, camera releases are leaked to the public beforehand so badly that someone would have to live under a rock not to know something is on the horizon.
There is the possibility of a firmware update for the 5DII to be announced around PhotoPlus time in October. Canon will keep selling 5DII's for quite a while. It is still the top for the specific features it has for stills and video combined.
Canonrumors.com is always the place to watch.
Simple question, if your 40D does the work fine and no client is demanding more, then what is the motivation to upgrade?
Two things mostly. The first, one of my clients mentioned they'll move to a minimum resolution of 12Mp within the next six months, so, my 10Mp 40D won't cut it anymore. Other clients are slowly following. Also, for advertisement today, I have to rent, and their minimum resolution is 21Mp (so, the 5D Mk2 would work just fine ). And next year I hope to be traveling to Thailand, where I hear electronics are really cheap ( compared to Brazil, not to the US of course ). The travel date isn't set yet, but it will happen sometime next year. It isn't a travel to buy things, but I won't mind to delay the trip a month or two to be able to get a new camera.
My current revenue doesn't justify replacing the camera every time a new model comes up, and it's forcing me to become a late adopter on cameras. So, I tend to stay some years with each purchase, as I do with computers ( around 3 years replacement schedule ). Considering that, and that a 5D Mk2 right now in Brazil costs around US$5600, I would hate to "burn" a trip to Thailand, where the camera is supposedly around 1/2 what it costs here, and see the new model coming up a few months down the road after that.
Of course, nobody has a crystal ball, and I still have a few months ahead of me to reach a decision, and only people within Canon know their gameplan. But planning helps, and yeah, if a 5DMk3 only comes out on 2011+, then I'd be safe to buy the Mk2... but if I notice there's a chance the Mk3 comes out in Photokina 2010 ( around september ) then I'd push the trip further away to see. I guess if that's the case, I guess rumor mongering would start about now, with leaks starting to spring around april, and the leak of the internal photographs starting in july... at least if my memory serves me right, is what happened with the Mk2.
Also, someone mentioned in another forum that a Mk3 is more likely to come out as a result from pressure by the Nikon models, and maybe there are already rumors of a 22+Mp Nikon model coming out soon within the 5D price range.
