Packing a Sid dCore.gz would be fairly simple, but running testing or sid system usually requires the means to update the system frequently, so it would an exercise in frustration for most to run a dCore made from it, even if the base libraries were up to date when the dCore.gz image was made. And base files sometimes change location between releases, which would make it unreliable to script.
Jessie (current Debian testing)is scheduled to be frozen on Nov 5th, which would says to me that sometime this summer that Jessie would be reasonably stable enough to base a testing dCore image on. Which would give us ample time to play with it and have it polished before the official release.