Note, there are HUGE SPOILERS for Avengers: Age of Ultron to be found below, so if you haven't seen the movie yet, then proceed with considerable caution (or, y'know, go out and see it. It's awesome).
Now, when it comes to the Avengers franchise, and the Marvel Cinematic Universe as a whole, conventional wisdom says that the most important part of the series is the the Holy Triumvirate at its center: Iron Man, Captain America and Thor. After all, the Marvel Trinity are - until this coming summer, at least - the only three heroes to have received a MCU solo-movie since 2008's relatively unsuccessful The Incredible Hulk. Add in big, green and angry, and there's an argument that - within the MCU - those 'big four' heroes are what makes the whole Marvel juggernaut tick.
Except, of course, they really aren't.
Instead, the secret to the whole MCU - from the first Iron Man all the way through to Avengers: Age of Ultron - has always been the small, personal moments between the leading characters...and the subtle, perfectly-crafted supporting characters who we actually end up loving the most.
That's how The Hulk and Loki stole The Avengers, that's how Black Widow (and The Falcon) stole Captain America: The Winter Soldier, that's how Rocket, Groot and Drax stole Guardians of the Galaxy, and, crucially, that's how Hawkeye stole Avengers: Age of Ultron.
Marvel Has Managed to Make Us Love the 'Smaller' Characters Way More Than You'd Expect
And yet, despite the obvious market for a Black Widow movie - there's not one to be seen anywhere on the horizon. Despite the love of the Hulk - and his widespread consumer-recognition - there's little chance of a solo-movie this side of 2020. And, despite him being a fan-favorite (and cheap) the odds of Hawkeye getting his own movie seem to be slim to none.
Unless, of course...
Marvel Just Set Up a Black Widow/Hawkeye Team-Up Movie
Y'see, there seems to be two main streams of thinking over at Marvel Studios at the moment. One the one hand, there's an apparent desire to expand the MCU out into different directions to ensure creative freshness (and box office revenue), with each upcoming Marvel movie seemingly a new, superheroic, take on an established genre. So, Captain America: The Winter Soldier is the Marvel conspiracy thriller. Guardians of the Galaxy is Marvel's space opera. Ant-Man is a heist caper. Doctor Strange a supernatural horror(ish).
Meanwhile, there's also a clear desire to keep everything firmly within the realm of the 'bankable.' So, Captain America: Civil War gets Tony Stark as a co-lead. Doctor Strange gets fan-favorite flavor-of-the-decade Benedict Cumberbatch as its protagonist. Captain Marvel looks set to get a superstar director.
And Avengers: Age of Ultron may well have finally lined up Black Widow and Hawkeye to fulfill those two (often conflicting) requirements at once.
Why a Black Widow/Hawkeye Movie Could Actually Work
Remember how - and this is where the BIG Avengers: Age of Ultron SPOILERS come in - we just met Hawkeye's wife, in what was arguably Age of Ultron's best twist? And how she and Black Widow are just as close as Clint and Natasha are, suggesting that the trio go way back?
Well, y'see, that opens up a whole lot more avenues for 'interesting, box office-friendly spin-off movies' than the previous hinting about 'Budapest' ever did - while at the same time playing a big part in transforming Hawkeye into half of the audience's new favorite character.
Combine that with the fact that Jeremy Renner and Scarlett Johansson are now both bankable stars in their own right, and you've got yourself every reason to believe that Marvel has their eyes on a Phase 4 movie with Clint and Natasha's names on it...
The Possibilities Are Endless
Want a Marvel version of Taken-style revenge thriller? Just have Clint's wife be kidnapped, and watch he and Natasha go rogue to (brutally) get her back.
Want a Marvel buddy-spy thriller? Team up a reluctant Clint with a family-less Natasha for classic buddy-cop antics.
Want Marvel's Mission Im...probable? Just add Maria Hill, Nick Fury, and whichever other Marvel heroes you feel like whose rights are just hanging around, gathering dust.
Want a Marvel Western? Just send Hawkeye and Black Widow back in time, and try not to have them run into Doc Brown.
The main thing, though?
It Seems a Hell of Lot More Likely Once You've Seen Avengers: Age of Ultron
Which might just suggest that Marvel already knows something we don't...