fridgerman the great
I have not found the Premiere Elements supports the Premiere Pro project file (prproj).
Now whether or not a Premiere Elements project file (.prel) is supported by Premiere Pro, that is open to question. According to the following Adobe document for Premiere Pro Supported Import Formats, PREL for Premiere Elements projects is supported for Windows Only.
Can you find a way to get the exports from either into one or the other program to achieve what you believe to be gains?