I assume you are talking about a A700 replacement in the long term, not some rumor A750 going around.
My feeling is there won't be a true A700 replacement. Instead we will see a PMA 09 an A500 which is much like it sounds, a slightly stripped down A700. It becomes the 1100-1200 model. And competes with the Nikon D90. They take the A700 as it is, remove a few things, maybe a slightly cheaper body, add off the main sensor LV and just minor stuff. It gives them an entry level body that is targeted at higher end/more traditional users. It has a real pentaprism, not a penta mirror, not movable display, just a more traditional camera. That all but kills A700 sales, but it's fine because come spring 09 when the A700 is do for replacement (18month theory) they will bring out an A701/A710 or how ever the system pans out for replacement models. This camera will be more like the Nikon D300. Everything that it gets knocked on, like not being super extreme tough, or not having a full coverage view finder so on and so forth gets upgraded. In many ways, it pulls stuff from the A900. So where sony had a $1400 camera straddling the Semi-Pro and Entry markets, now it just becomes 2 different models. One higher, One lower. Clearly to have 2 models like that wouldn't have been an option early on for Sony, the A700 had to be a compromise. Now they can have a A710&A900 that match up much like the Nikon D300 and D700. Similar market, similar design, but have the differences between APS and FF, mainly the 1000-1200 USD price differance.
So what ever the A900 has, expect a fair bit of trickle down.
For a sensor, an A500 might do as David says and go for the 14MP CCD, or stick with the A700 sensor. I think we will know more when the Nikon D90 comes out. We will know if there is a new sensor, or it's the A700 sensor, or if Nikon had implemented the 14MP CCD and we find it has LV capability. My money would be on an A500 having the 12MP sensor. Where an A700 replacement gets an all new sensor. Probably a 14MP CMOS unit, Sony addresses how they did NR and the read out (they could probably just use the current sensor as is and just use it differently). But cameras will keep gaining 12MP at time, so they grow there. I don't see any way the CCDs will end up back in the higher end models.
The 14MP CCD could be a one hit wonder. It is probably the result of a continued design on the old CCD architecture while sony created the new CMOS chips (A700/D300/A900). I highly doubt Sony would keep using a sensor if they can't get Nikon or Pentax to buy it. Seeing that Pentax went 14MP in the K20D, there is probably a good chance that Pentax had Sony and Samsung putting in proposals for 14MP and Samsung won. So Sony is probably not going to sell it to them. And if the D90 sticks to the D300/A700 sensor, and the D60 is still on the 10MP CCD, there might just be no market for that sensor. Unless there is a D60X in the works, it could have just been Sony deciding to put it in production after all their effort, slap it in the A300 but make it a higher res option, see how it does and re-group.
But focusing back on the original question more. I just don't see a true replacement, a new $1400 model. The A700 came out several months before the A300/A350 and carried Sony for a while. They really need a model that falls between (A500), which leaves no price range for a 1400 model. At the same time, they need to do something with the D300 and future D400. So it needs to step up on a replacement.
I suspect Canon will be working on a similar path. They either need to re-invent the #0D line or make it official and starting with the 50D just say it's entry level camera and market it against the D90 and what ever Sony brings. In the mean time, they need a "7D" (yeah, I said that, but Canon world is full of said rumor a lot). A "7D" being the APS brother to the "5DII". Gives canon a similar setup to the Nikon D300/D700 setup. Or Canon simply needs to re-invent it as I mentioned and bring a 50D that packs the works and cost 1600-1800 to go against the Nikon. As is, if a 5DII comes out at $3000, and the 40D is nearing $1000, that is a massive gap with no camera. So they need to do something. Sony will be in the same boat if they don't make a higher spec replacement to the A700.