I couldn't find a definitive answer on the Conroe's logic board compatibility.
I would hate to see a crippled semi-pro configuration like the 4 DIMM 1.8 and Rev C 2.0 PowerMac G5's, but it could be a possibility.
Since Apple will want to keep the prices down on iMacs, any requirment for FB ECC RAM would be inconvenient to say the least.
At least until FB ECC RAM goes mainstream and the prices drop.
This should prove to be an interesting revision.
With Core Duo 2 processors and a decent video card, you already have an iMac AOI that competes quite honorably with my Pro 8 DIMM DP 2.0 G5.
One blessing in the court of a 23" iMac would be 4 DIMM slots, allowing the
user to upgrade to 4-8 GB RAM. 4GB RAM would be plenty enough to handle most Pro applications.