(Warning: The following contains potential - albeit entirely speculative and comic-book-based - SPOILERS for future Marvel movies. Proceed with whatever level of caution your future-seeing Inhuman buddy Ulysses suggests to you is wise...)
Now, when news hit a few months back that Marvel Studios' long-awaited Inhumans was being delayed - and now had no confirmed release date to speak of - many fans were concerned that the movie wouldn't actually be making it to the big screen at all. With other projects vying for the limelight, and the Inhumans being a largely unknown quantity, despite Agents of S.H.I.E.L.D.'s best efforts, it seemed entirely possible that Inhumans could be disappearing for good.
Thankfully, though, that doesn't seem to be the case - and not only because folks over at Marvel Studios made sure to reiterate their support for the project. Y'see...
The Inhumans Might Just Be Set To Define The Whole Of Marvel's Phase Four
Now, there are a whole lot of ways that Marvel could go with its next 'phase' of movies - the current Phase Three is just beginning, and looks set to run through till the end of 2020 - but one of the most intriguing may well be far more Inhuman-centric than the teams delayed arrival might suggest. In fact, it's not impossible that the delay has as much to do with long-term narrative planning as it does with scheduling logistics.
Phase Four Could Well Be Defined By Earth's Interaction With Space
After all, with the distinctly space-centric (in the comic-books, at least) Captain Marvel set to see her own solo movie arrive in 2019, and Avengers: Infinity War, Pt. 2 all-but certain to introduce Earth's heroes to the galactic pleasures of outer space, there's a pretty good chance that the MCU will be looking to space long before Phase Four arrives. With a Guardians of the Galaxy sequel also tipped to be a key part of the early 2020s Marvel slate, it seems entirely plausible that we could see much of the MCU move space-wards, thus taking advantage of the likely Star Wars-prompted boom in sci-fi adventure-related interest.
And, if so...
The Inhumans Are A Natural Crossover Point Between Earth And Space
Y'see, with the Inhuman royal family (above) traditionally being both from space (they're traditionally the descendents of alien science experiments) and Earth-born (those experiments were on ancient humans, and they've largely lived on Earth ever since), they'd be an obvious next step on the Star-Lord scale of alien-introduction.
After all, while the Inhumans we've been seeing in Agents of S.H.I.E.L.D. have largely been Earth-based, there's no reason to believe that the introduction of the Inhuman royal family would hold to the same formula. Indeed, with decades of celestial excursions in the comic-books behind them, there's every chance that we could see the Inhumans' big hitters turn up on Earth to support their terrigen-mist born pals, and opt to reside there - thus creating a classic 'fish out of water' story-line. If they were to do so, however, it would likely create a Phase Four-spanning plot-arc, with the heroes of the MCU (and its governments) being forced to deal with what is essentially a minor, possibly benevolent, alien invasion.
In other words?
There's a Pretty Good Chance We'll See The Inhumans' Actions Impact Upon Every Other Movie In Phase Four
So much so, in fact, that there's every chance that the final movie in Phase Four (a triumphant return for the disbanded-in-the-wake-of-Infinity War Avengers, perhaps?) could see Earth's mightiest heroes taking on the Inhumans in an epic battle...before being forced to work alongside one another to face an even larger threat.
After all, there are even bigger threats out in the Marvel comic-book universe than Thanos...