Let's skip the FS2004 vs FSX debate, it's not even relevant.

I have both, and also have the CS 707, 727 and 757 for FS2004. I've been using MSFS since FS2 and I don't like losing planes/scenery when upgrading. Not all my addons work in FSX, nor do they have replacements and this includes the CS 707! For that reason I'm sticking with FS2004 as my main sim for now.

Point is there is still plenty of interest in FS2004 so I would ask CS to reconsider releasing an FS2004 version of the 767, possibly even with reduced functionality compared to the FSX version if need be. I don't see how this would set back FSX users in any way: the FSX version is already available.