It should be possible. Have you tried?
Actually, within a somewhat narrow range, you CAN Open PrE Projects (PREL files) in a contemporary version of PrPro. For instance, I can Open my PrE 4.0 PREL's in PrPro 2.0. When you get several version numbers apart, it might not work. As a for instance, I cannot Open PrE 7, 8, 9 or 10 PREL's in PrPro 2.0, but PrE 9 PREL's do Open in PrPro CS 5.
One thing to remember, however, is that PrE has some features that do not exist in PrPro. Examples will be Themes/Instant Movies, NewBlue FX Effects/Transitions, etc. If you have used any of those features, you will loose them, when you do Open the PrE PREL in PrPro. Note: PrPro Projects (PRPROJ files) will NOT Open in PrE. These same limitations also exist when Opening older Premiere, or PrPro Projects in later versions - some of the older versions had 3rd party features, that do not exist in later PrPro versions, but the program is pretty neat, in that it will tell you of, say a missing Transition, will tell you the TimeCode where that was used, and also give you the name of the missing Transition. Effects can be a bit tougher.
I cannot comment on AVID, or FCP, but I would rather doubt that the PREL's will Open in those programs. Maybe someone with those, plus PrE, can comment.
Now, PrPro does offer some X-program support, with features like EDL's, etc., but PrE does not support those.