The issue is on using previous versions of VFP at the same time as the new upgrade version. You can go back and forth between the new version and the older version(s). So there really shouldn't be any issues for anyone, it is the same as it was for VFP 7.0. This is not a “new” change for VFP 8.0. This has been in Microsoft EULAs (including Visual Basic/VC/Visual Studio/VFP) for many versions. This is also same across various other groups at Microsoft. You should really look at upgrade and downgrade rights in tandem. You can always go back to using an older version because of your “downgrade” rights. The intent of the “upgrade” is that you should move to using the new version within a "reasonable time" if you paid Microsoft “upgrade” price (i.e. discounted) as opposed to full price. Again, the EULA is basically the same as it was for VFP 7.0. From the VFP 8.0 EULA...

11. UPGRADES/DOWNGRADES
11.1 Upgrades. To use a version of the Software identified as an upgrade, you must first be licensed for the software identified by Microsoft as eligible for the upgrade. After upgrading, you may no longer use the software that formed the basis for your upgrade eligibility.
11.2 Downgrades. Instead of installing and using the Software, you may install and use copies of an earlier version of the Software, provided that you completely remove such earlier version and install the current version of the Software within a reasonable time. Your use of such earlier version shall be governed by this EULA, and your rights to use such earlier version shall terminate when you install the Software.