Brackets in a quote denote a change to what was actually said. In a perfect world, with quality journalism, they're used to summarize or make the quote flow better in the piece without changing the intent or meaning of the quote

In this case, they very well could've changed "won't be" to "will be"

I don't expect that to be the case here, but it's possible.

Also, using an ellipsis inside brackets like this: "[...]" Is an intentional omission by the author of the piece.