EDIT2: Remember, the only reason people have been suggesting that a 21mp 5D replacement is going to happen is based purely on Sony's entering the full frame market.
There are a few points to remember about Sony's full frame entrance... Firstly, Sony haven't really proven themselves as far as professional photography is concerned... We all watch with a keen eye, but there haven't been a whole lot of 'pros' who've made the switch to them at this point.
Delays are NOT beyond Sony... While they've lead us to believe we'll definantly see their A900 this Photokina in its final or near final trim, there's no reason we'll see it on the market in due time. While the gaming devision is a seperate entity really, the PS3 was delayed substantially, and working prototypes and models were already out more then a year in advance. Even now, the console has very little as far as unique gaming is concerned.
12bit DAC... There's a lot to say about this point, and while it may not be the ultimate deciding point, a lot of people who are interested in the 5D and above, understand the possitive aspects of a 14bit DAC (except those who shoot mostly JPG). The Sony sensor is a 12bit DAC sensor, and while it's been a norm in the 35mm industry up until recently, it may be seen as outdated.
I think the word on the street is that the Sony A900 is supposed to hit the shopshelves right around the time of announcement (around a week or so away). Dozens of Sony reps have already handled the finished version, worldwide (multiple continents). There are also talk that Sony is in fairly advanced stages of picking up some companies that will effectively function along the lines of the Canon/Nikon Service centers, specifically for their Alpha dSLR line.
I think the body with its 25MP sensor, and a 100% viewfinder and estimated 5FPS at its full resolution, with its built-in IS, is supposed to hit the ground at a sub-$3K pricing, which makes it pretty interesting, when one can pair it with the class leading lenses like the Carl Zeiss 24-70 f/2.8 SSM Vario-Sonnar (PopPhoto rated its resolution and micro-contrast higher than even the new Nikon 24-70 f/2.
and/or the 24-105 f/4 G SSM (expected to be announced) and the Carl Zeiss 16-35 f/2.8 SSM Vario-Sonnar (expected) and maybe a couple of Zeiss primes with AF, like the 85mm f/1.4 Planar or the 135mm f/1.8 Sonnar. Also expected are several Zeiss and "G" primes in the 35mm f/1.4SSM, 24mm f/1.4SSM etc specification. There is also a rumor that a Carl Zeiss 70-200 f/2.8 SSM Vario-Sonnar is also in the final stages of development.
In addition to these, remember that the upcoming longer lenses like the 600mm f/4G SSM along with the 70-400 f/4.5-5.6G SSM etc are all 2008 designs that have been benchmarked and specifically designed for high pixel density Full-frame sensors, with terrific telecentricity, corner-to-corner high-performance on FF Digital sensors and specific optimization for Digital sensors.
I think the whole package of Zeiss lenses above, with the A900 body, would come in at a price that is roughly the same as the 1DSMKIII body alone. That is pretty tempting, especially when one can have stabilized shots with one's 50mm, 85mm and 135mm primes. The price is cheap enough that it might even tempt some people to shoot dual-system for a while.
But you are right. Sony is yet to be a "proven" force in the professional 35mm landscape, like Canon and Nikon but I doubt a giant like Sony, with its sheer breadth and depth in electronics par none (touching every aspect of the "D" in a DSLR), picked up a traditional camera company like Konica-Minolta, to sit around and play in the side-lines for too long. Every single one of their introductions (including the upcoming A900) have been dot on schedule over the 2 years that they have entered this business, with the availability of the product on shopshelves, almost immediately after the announcement of the product.
All I am saying is, competition is nice. The more competition that exists, the less the possibility of Canon sitting on its backside, like they did with the 5D over the past 3 years with absolutely no update whatsoever to the product. Also, you can bet your bottom dollar that the ONLY reason you are finding the 21MP FF sensor in the upcoming 5DII, with FAR more advanced specification than they normally would have added into it, is specifically due to the long shadow cast on it, by the Sony A900....the decision by Canon is not a coincidence by a long shot.
