The solution to this meta are the four letters (top-left, top-right, bottom-left, bottom-right) that make valid (5) letter words on the perimeter of the crossword. They are not proper nouns.
nice - i love the corners puzzles! this is a very cool concept... do you think you can make one where the meta answer spells a word? i feel like it's possible, but it would be extremely challenging since the three letter answers still have to be valid fill hmmm