There are ways to import the old style (FS98/FS2000) mdl files into the design programs.
If this were extended to the newer models made with gmax and FSDS2, you would see a sudden drying up of quality freeware models and an increase in file protected payware.
After all, it it becomes easy to take off someone else's model, change it a bit, and pass it off as one's own work, what is the incentive to produce quality work?
"IF" the *.mdl files were to "EVER" be successfully imported to Gmax or FSDS, then there would be a very good chance that M$ might change the FS series from open-source to closed-source (like the IL-2 series of 1C: Maddox Games).
As a result, we would all be greatly affected by such a sudden change. I thank god that no one has broken the code. And I also pray to god that no one ever does so ,successfully. Because I don't won't to see the negative effects of cracking such a code (like the one that Felix pointed out).