The problem with this interpretation is that it proceeds from a false premise of "Creatio Ex Nilho" (Creation from Nothing) which was a concept that arrived on the scene with Platonic philosophy This is not to say that this philosophy is wrong (matter had to come from somewhere and have a beginning after all,) but simply that it does not apply to this text which was written from a perspective of "Creatio Ex Materia".
This is not to say that this is not, in fact, how God created, just that the text of Genesis was not written from this perspective. Under that assumption, the question becomes, what is creation? The etymological meaning of the verb בָּרָא (bara'), is "to cut out and put into shape,". Therefore, though akwardly worded, the earth could become formless and void ("Creatio Ex Nilho") and then be created ("Creatio Ex Materia"). In this way, it really wouldn't matter or impact the meaning of the text if it says "became" or "was".