That's right, despite the heroics of Eleven and the gang, danger and demogorgons are never far away. Let's go through what happens in the mid-credits scene, and what it might entail for our lovable, bike-riding misfits.
As Dustin would say, it's time to unlock this curiosity by, but of course: Spoilers ahead .
In the dark, icy plains of "Kamchatka, Russia," we see what appear to be the domed buildings of a military facility. In one of them, two Russian soldiers stop to unlock a steel door. "No. Not the American," the second soldier says, no doubt a massive hint our favorite police chief is still alive and well within, but more on that below.
The soldiers instead move on to the next door, clanging it open to reveal a haggard prisoner who begs in Russian not to be taken. Swiftly ignoring him, they drag him down to a cage, where one of the soldiers cranks a wheel that opens up a metal hatch. Out prowls what appears at first to a brawny, goo-slobbering demo-dog, until it proceeds to stand up on its hind legs as a fully grown demogorgon. It has its four Venus flytrap flaps for a head and the prisoner is forast
What it means
First and foremost, it's pretty clear there are more Demogorgons knocking about. While defeated the Demogorgon terrorizing Hawkins in season 1 and sealed the town's gateway between 2 and 3 dimensions, it is honestly not surprisingly more monsters have crept through from the Upside Down.
The Demogorgon in Russia suggests another wound between dimensions has been opened. That would allow the Mind Flayer, controller of the Demogorgon hive from his home in the Upside Down, to continue its plans for world domination. This is assuming there's only one Mind Flayer. Dustin befriending our favorite loyal Demo-Dog Dart. It is the Cold War, after all.
More Russian military
The Russian military may be done with trying to take advantage of the gate to the Upside Down under Hawkins. We now know they've been experimenting in Kamchatka, which is in the real world is a remote, volcano-filled peninsula in Russia's Far East. During the Cold War, it was developed as a secret military region that had prime positioning across the US.
Could a mission to a military base on lockdown overseas be in the cards for season 4? It is difficult to imagine how it works, as smart and powerful as they are, biking their way through that one. Hawkins' interdimensional gate is more likely to be further exploited from the Russian military.
Hopper's still alive
At the end of season 3, Hawkins' resident unsmiling police chief plays a crucial part in stopping the Russians from tearing up the wound to the Upside Down. While Hopper struggles with the relentless Terminator-esque Russian officer down by the energy drill, Joyce is up in the control room cutting off the power. In the ensuing energy surge all the hazmat scientists exploded in blood and guts. Joyce stares at the spot Hopper had been in, but he's nowhere to be seen.
Crucially, there's also a sign of Hopper's blood and guts, so that leaves his possible death open. Again, the line from the Russian soldier – "No. Not the American" – heavily suggests he's been captured, while Russian soldiers cleaned up their botched mysterious doings. As for speculating about Hopper's future, a healthy dosage of torture and manipulation is probably in the cards.
There's also the matter of David Harbor's future projects, which probably won't see him on a huge Hollywood franchise with. The determinedly-gated R-rated film bombed with critics and the box office, despite Harbor Shining as the Red Devil.
Harbor seemed to confirm the franchise's fate when it appeared on the possibility of a sequel in June. "I don't think the perception was that it was a hit, and so in that way, I don't know that the risk is worth it," he said.
Will we see Hopper again? Whatever the case, creators the Duffer Brothers have suggested Stranger Things will wrap up the stories of our rapidly growing young heroes after a fourth or fifth season.