I'm not a still photographer (though I wish I had some formal training in photography!) -- my focus is video and film. From what I see, the 5D Mark II is obviously selling very well and getting a lot of free advertising from leaders in the DSLR film movement. However, there are also many flaws as some have noted:
- Poor HDMI ports/location of ports/HDMI connectors break easily
- Drops to 480p when using external monitor
- Main LCD not viewable when monitoring
- No HD-SDI monitoring support (need converters, which are a pain)
- Rolling shutter when camera is moved quickly
- Occasional aliasing, moire, and line skipping
- No 1080p or even 720p at 60fps (therefore hard to use for slowmo)
- Poor audio and controls
- Good in low light, but not as good as Nikon
- Only 1080p -- not 3k or 4k; No "raw" video mode
Still, despite all these problems, there are TONS of budding filmmakers buying or renting 5Ds -- and Canon is getting lots of free exposure and marketing.
However, most of these people are not totally loyal to Canon -- just to the best camera for their needs. So if a competitor comes out with something better (i.e. Panasonic, Nikon or even the ever-delayed Red Scarlet) ... they could have customers jump ship.
Also, there are many many people on the fence -- unsure of what to buy, or wondering if/when Canon will come out with something better.
So with the explosion in using these cameras for film -- if they released an update for the 5D soon that solved all these issues ... it would be the "ultimate" indie film camera. And an important step forward for pros like those who shot House on the 5D or Lucasfilms, who are beginning to use it more.
Thus, the strategy behind releasing a 5D3 soon would be to get so many new people on board who would also buy lots of lenses and other stuff, specifically for Canon. This would make it harder for someone to switch to Nikon or Panasonic later.
In a sense, I'm in this boat. I'm about ready to buy a 5D, despite it's issues, because it's still the best camera in its price class for my needs. And I'll also probably buy about $4,000-5000 in Zeiss Prime lenses in Canon ef mount.
Oh well ... no matter what, it doesn't look like they will be releasing the new 5D in time for me to wait -- so I will most likely get a current 5D2 and then sell it at a steep discount or use it as a "b" camera when the new one comes out.
Or .... (fingers crossed) the 1Ds will actually solve all these problems, come out in the next 30 days, and retail for the low, low price of just $4997!!!! ;-)
But given everything I see on this board, that seems about as likely as the Red Scarlet coming out soon!