Will this be the next major passing record to be broken? I say "YES." There have been a total of fourteen 500 yards passing games in NFL history. Six of those games came within the last six seasons, including two in the 2011 NFL Season (Tom Brady, Matthew Stafford) and two more during the 2012 NFL Season (Eli Manning, Matt Schaub).
It would be pretty easy to pick Brees, Brady, Aaron Rodgers, or Matthew Stafford, to break the record, but I wouldn't be completely surprised if a relatively unknown or a backup quarterback sets the new mark. Last year, Cam Newton set just about every rookie record including the most passing yards in game with 420 yards in his very first game. He followed up the next week by breaking that same record with 430 yards. This year, Andrew Luck broke Newton's rookie record for most passing yards in a season with 4,374 yards. In 2011, even Green Bay Packers backup quarterback, Matt Flynn, had his share of the action with 480 passing yards against the Detroit Lions. That was the same game Stafford threw for over 520 yards.
With all that said, I think Drew Brees will set the new record. He'll do it while becoming the first player in NFL history to throw for more than 600 passing yards in a single game.