The big announcement in August will be for a new Nikon D4 and D400 DSLR cameras. The Nikon D700 replacement will probably be announced at a later date, maybe even in 2012. I know that this is not the news most of you want to hear, but it actually makes perfect sense because the Nikon D3 was announced together with the D300 back in August of 2007. Nikon is a very methodical company and if the D3 and D300 pro level DSLRs are on a 4 years life cycle, the D700 should be replaced in 2012 since it was announced in 2008. Nikon also likes to announce higher end models before using the same tech in a low end versions (for example 12MP DX sensor in D300->D90, 16.2MP DX sensor in D7000->D5100, 12MP FX sensor D3->D700), so don't expect the Nikon D700 replacement to come out with a better technology before the D4. The D300s replacement will probably use the new 24MP sensor from Sony which further confirms this rule.
Another question here is: does the "S" update count as a replacement? The D3 and the D300 were "replaced" by the D3s and D300s but for the most part those were just minor updates. The D3s and D300s were announced in 2009, approximately two years after the D3/D300. There was never a D700s. Maybe there is still a possibility for a deviation of the D700 this year (let's say D700s: D3s sensor + video), but my source was clear that the "real" D700 replacement will come out in 2012.
[NR] probability ranking: 70%