A good idea in theory, but it's not practical as the cost to maintain the code would eventually become prohibative.
To show you what I mean, let's just pretend that the world began with NX 1 (it actually goes back to V11.0).
OK, when we finished with NX 1, there was no work to do since there was no 'old' versions to go back to.
Now we finish up with NX 2 and we have to create a converter to go back to NX 1. Extra work, but probably not a big problem.
However, after finishing up NX 3, we have to create the converter to go back to NX 2 AND update the code for NX 1.
And after NX 4, we have to develope the new code to go back to NX 3, as well as update BOTH the NX 1 and NX 2 versions of teh code.
And finally after NX 5, we have to develope the new code to go back to NX 4 and update the other 3 versions, for NX 1, NX 2 and NX 3.
And know that there's going to be an NX 6 and hopefully an NX 7 and 8 and 9 and ...
Notice a trend here? Now think what this would be like if after we had finished NX 5, we would have had to go back and account for all 13 legacy versions of UG/NX.
Image what the level of effort could grow to when you consdier that at each new release, dozens of new feature types created or major changes to existing ones, that would have to be mapped back to the hundreds of object types already in the legacy versions of UG/NX.
To show you what I mean, the following are new Features or significant changes to existing Features that were added in NX 5 and which would have to be accounted for when moving back to a legacy version.
Point between points.
Blend end caps.
Face Blend across non-tangent faces.
Instance Geometry.
Features across mulitple bodies.
Multiple draft angles in Extrude.
Trimmed Sheet.
Law Extension.
Sketch Offset Curves.
Circuler Blend Curves.
Thicken.
Untrim.
Unsew.
Offset Emboss.
Assembly Constraints.
JT Facets.
And this doesn't include any changes to expressions, attributes, drafting, etc.
Anyway, I hope you can start to understand why this would be virtual impossible task to accomplish, release after release after release, with any hope of maintaining any kind of long term reliable code that would continue to output robust data based on a growing list of legacy versions, each with their special issues, constraints and limitations when compared to the changes in the latest versions of NX.
John R. Baker, P.E.
Product 'Evangelist'
UGS NX Product Line
SIEMENS
UGS PLM Software
Cypress, CA