According to perldata,

For compatibility with older scripts written before __DATA__ was introduced, __END__ behaves like __DATA__ in the toplevel script (but not in files loaded with require or do) and leaves the remaining contents of the file accessible via main::DATA.

So, I wonder if an __END__ in a .pm file will not have the unwanted side effect of holding that file open, like it does in the main file. This is good news for those who want to continue putting the pod at the end.

—John