Looking at the negative atmosphere surrounding internet crowd regarding new Avengers I'd be surprised if it won't bend up being the biggest flop in the history.
Movie will probably have combined budget approaching 1 billion.
And looking at every MCU movie underperforming or flopping what are the chances people will go to the theaters to watch Avengers they have no connection to? Surely Marvel will brute force someone butts into seats with aggressive advertisement like WB did with Superjew but will it be enough to make even 1.5 billion?