IMF Is Back, Ready For Mission: Impossible 7
But, as has already been alluded to by Simon Pegg, Mission: Impossible - Fallout isn't the end of IMF. Indeed, with the recontextualizing of Ethan Hunt, the series has essentially created a blank slate for the future. Hunt is known and his biggest emotional hangups have been addressed, while the specific focus on the team makes clear that IMF - which is now without a leader after the death of Hunley - is set to be an ensemble effort. With this playing field, Mission: Impossible 7 can pretty much do what it likes.
This return to a status quo after a self-justifying adventure is very similar to what James Bond recently attempted with Skyfall and Spectre, although considerably stronger. There, while the first was an undoubted success, the second proved too confused over what it wanted 007 to be; it was Dark Knight seriousness mixed with throwback humor and a reflective plot just like Mission: Impossible - Fallout, but there was no cohesive throughline (best seen in its return to status quo moment instead seeing Bond run away). By this comparison, not only does Fallout provide a thoughtful look at what the franchise is while telling a new adventure, it reconfigures to give the future best freedom.
The Apostles Are Still Out There
That said, there are still some key plot aspects out there that can - albeit needn't - be explored in a Mission: Impossible 7. The biggest, of course, is the Apostles, the remnants of the Syndicate. John Lark is dead and Solomon Lane is now under the watchful eye of the British, but the many other rogue agents are still out there lurking in the shadows. Note that their faces weren't shown, leaving ample opportunity for adventurous casting in the future.
We also have the White Widow (and her brother). Another British femme fatal, she's revealed to be allied with the CIA in the final moments, placing the character firmly in the morally ambiguous category. With a familial connection to Vanessa Redgrave's Max from the original Mission: Impossible, this is a new area very easy to return to.
Mission: Impossible has always shirked massive, overarching continuity, with Fallout the first time the story has continued from the previous entry, and even that was broad (another problem with Spectre in comparison - it took narrative threads instead of thematic ones). However, in establishing a clear grand antagonist and continuing to build the world, the series can gain some sense of purposeful structure as it enters its third decade, with at least some vague pre-plot justification for the 56-year-old Cruise continuing to accept the mission. And, now Ethan Hunt knows his greatest strength, less than nothing is stopping him.