I don't think it would be too hard, but it would be important to associate it with a post-processor.
If those other packages are importing successfully without knowing what machine the file was made for, they were just "lucky". Lucky, in the sense that the file only contains G0 and G1 commands, so it's as generic as a g-code file could be.
Even if the file didn't have the G91 call to identify incremental mode, there's a pretty simple statistical analysis of the vectors generated by g-code that will tell you if it's an incremental or absolute file. With incremental files, if they are treated as absolute, many, many cutpaths will pass through a small circle surrounding the origin, while absolute files seem to "go somewhere", so to speak. Of course, your file DID have a G91, so it was pretty easy to tell... but still interesting to look at what it generates when treated as an absolute file.
I don't think this is a job for a change in CB, though. This should be a script or plug-in, at least at first.
If I had time to ferret out all the structures in CB, I'd write it myself (but NObody is HELPing document the plug-in writing process for us TIME DEPRIVED users who WANT TO HELP!)