One thing that seems to come up constantly is the desire to have some sort of backwards compatibility between releases of SolidWorks. It is mentioned on the various SolidWorks forum message boards at least once month (and sometimes almost daily).  Why does SolidWorks not provide for backwards compatibility. Well, the cynic will tell you that it is intentional, as part of the overall SolidWorks Corp business model. Others will say that it is due to new features and tools being added to each release which will not be supported by previous releases.
Right now, I cannot speak to reasons relating to business model. I can say that the SolidWorks development team, some of which attended the T-VSWUG Sept 10th meeting, seem genuinely interested in users’ desires and ideas regarding backwards compatibility.Â
One suggestion at the meeting was to provide a way to simply save models for older releases. The problem here is that once an unsupported feature is reached in the FeatureManager, it and all subsequent features would have to be dumb anyway.  On the other hand, the advantage is that as least some of the information in the model would useful.
Another suggest that had been on my mind was actually proposed by the SW development team; open, edit and create files native to their release level within a single session of SolidWorks. Features and functions not supported by the release level of a particular model would either be grayed out or (when selected) display an error message stating that it is not compatible with the release level of the active document.
You know what? I like this approach best. I can image there are some technical issues which will need to be over come. For example, how will SolidWorks handle assemblies with mixed release levels? Regardless, it seems the SW development team is on top of this issue. Hopefully, a working solution to this issue will be available sometime soon (2 years?).