With the recent announcement that Sony is moving ahead with a standalone Venom movie for release next year, there are a lot of questions about what form it might take. There haven't been many answers since then, either; even the initially-reported director has since been disassociated with the project.
Along with the announcement of the movie came a rumor that it would exist in a separate continuity from the Marvel Cinematic Universe, which would place it separate from Sony's upcoming Spider-Man: Homecoming as well. A lot can change between now and next year, however, so it's possible that Venom will end up having an MCU connection after all.
Since we don't really know for sure, here are all of the possible connection types that Venom might have with the MCU.
If initial rumors are to be believed, Venom will have no connection to the MCU and will instead create its own continuity. This could lead to additional Spiderverse spinoffs at Sony in the future, possibly reviving the company's previously-abandoned plans for a Sinister Six movie as well. This would be similar to the way Warner Bros. approached a Catwoman film with Halle Berry in 2004, though hopefully with a better overall result.
This route would give the studio the greatest amount of control over the film (and any additional spinoffs that might occur in the future), since they wouldn't have to worry about MCU continuity. Unfortunately, it would also have the most potential to confuse fans since Spider-Man himself is now rooted firmly within the MCU. Either Venom would take place in a world without a Spider-Man (which may sound confusing, but you have to remember that Sony was once planning an Agent Venom film before Venom himself had been introduced) or there will be two sets of cinematic Spider-Man lore to keep track of.
Of course, there are a few things that Sony could do to make things a little easier to keep track of. Assuming that the Spiderverse includes Spider-Man, Sony could always go with the Miles Morales version of the character to keep its films separate from Marvel's.
Depending on Sony's plans with Venom, it's possible that the studio could seed in some weak connections to the MCU to leave its options open for the future. This could let it be a "connected" property if it wanted to integrate with the Marvel films later without adding in all of the baggage of directly connecting to Homecoming and other Marvel films.
This would work similarly to how Marvel's Netflix shows reference the MCU films, with vague descriptors such as "the green guy" being used in place of actual character names and "The Incident" being the nondescript name given to the event of the first Avengers film. Venom could use similarly vague language to reference characters, places or events from the MCU-connected Spider-Man franchise or other parts of the Marvel universe.
If the decision was later made to bring Venom into the fold as a proper part of the MCU, other films could reference the events of it or other parts of the Spiderverse (assuming that Sony moves forward with other spinoffs or connected films after Venom). This would let Marvel and Sony test out and tweak the Venom character before bringing him in as a Spider-Man villain in a future MCU movie, especially given how poorly the Topher Grace version of the character was received.
If Sony and Marvel decide to bring Venom into the fold between now and its release date, the studios could work direct references to MCU films and events into the movie. The most obvious would be references to the events of Spider-Man: Homecoming, though references to the Avengers films or other Marvel characters could fit in as well. While cameos could be possible, they would likely be last-minute affairs and relatively brief in scope. The most likely candidate for a cameo in Venom would of course be Stan Lee.
Any such connections could be added fairly late in the game through the use of reshoots, adding in a few lines of dialog or other references as needed. Depending on how strongly the studios wanted to connect Venom to the other movies, a post-credit scene featuring Tom Holland's Spider-Man or some other direct connection to the existing MCU could be added relatively late as well (and possibly filmed in conjunction with the currently-filming third and fourth Avengers films).
Moving forward, references to Venom could be integrated into a Spider-Man: Homecoming sequel as well. Eventually, the two franchises would likely collide with Venom taking the role of the villain against Spidey.
Does Venom Need to Connect at All?
Of course, the big question is whether Venom really needs to connect to the MCU. If it stays separate, it could give Sony an easy inlet to the increasingly lucrative R-rated superhero film market. It would also help to protect Marvel in case Venom goes off the rails and ends up being a Fantastic 4-sized flop. Sony's track record with Spider-Man films has been pretty hit or miss in the past, and it's unclear whether the studio could turn it around with the villain-turned-antihero.
That said, if Marvel embraced Venom it could be interesting to see what the two studios could do working together on the project. Venom has only had the one adaptation so far, so there's a pretty wide margin of error when it comes to adapting the character in a new film (basically, just don't do what Spider-Man 3 did). Even if Marvel just provides guidance at this point instead of embracing Venom totally, it could set the stage for a well-developed villain to take on one of its most popular new characters in the future. There are certainly worse possibilities.