Why we shouldn't get our hopes up for 2v8
I would love to see 2 killers vs 8 survivors as a game mode in DBD but we should accept that it won't happen any time soon for a number of reasons.
1. MAPS: doubling the players would require a doubling of map sizes, especially for 10 gens to spawn. And I'm no expert, but I don't think it would be as easy to squish to maps together as people think. Plus, since you'd want maps to be the same realm (imagine The Game attached to Haddonfield- balance aside, it would just look weird) that would limit maps to Macmillan Estate, Autoheaven Wreckers, Coldwind Farm, Backwater Swamp, Red Forrest, Crotus Prenn Asylum, and Yamaoka Estate. 7 XL maps is a lot to make, but not a lot to play in.
2. KILLER PERKS: Right now, killer perks are all based off the assumption there is one killer and therefore no duplicate killer perks. But let's take, for example, one of the most common killer perks: Hex: Ruin. Now imagine if there were two killers running Ruin. How would that work? Answer: it wouldn't without the perk being reworked, and the same goes for so many other killer perks. With 10 totems, Hex: Thrill of the Hunt would double in power. Would Thanatophobia still be capped at 4 survivors? And even with ones that make sense balance wise, they would probably require a lot of attention because they were made with there only being 1 killer in mind. Reworking killer perks would be a massive task for the devs.
3. KILLER COMBOS: Certain killers would be able to unfairly combine their powers. For example, imagine going to a jigsaw box and seeing a bear trap at the interaction point. Not only do you have to disarm it while the trap on your head is counting down, but you tell both killers where you are. Heck, with Amanda's Letter, once a trap is on someone, the killers could just go afk in front of both boxes and be guaranteed a kill. Devs would either have to remake most killers to be balanced for 1v4 and 2v8 or create a separate version for 2v8. Either one would take a lot of time. That said every killer combo has fascinating potential synergy and I might make a separate post on this later- lemme know if that's something you'd like to see.
4. OBSESSION: This would be another unique problem, namely: do you have one shared obsession between killers or two that are independently tracked. The first option would not only be weird for lore (DSing killer A makes killer B mad) but also make perks like Dying Light and Remember Me a lot more powerful, since they would affect 7/8 rather than 3/4. The second option would just be tricky to implement well. How would you show which survivor is which killer's obsession? What if one killer has obsession related perks but not the other? In this scenario, if both killers ran Dying Light you could be buffed and debuffed by it simultaneously. Either way, many perks would need to be changed, which is of course more work for the devs.
5. AUDIO: This is just a small thing, but say you're near The Oni and The Demogorgon. Overlapping music! In fact, overlapping heartbeats in general would be confusing and chaotic. Finding and implementing a solution would be, you guessed it, lots of work for BHVR.
6. LORE: This isn't some game breaking potential exploit, but lots of killers wouldn't be cooperative. If The Huntress killed German WW1 soldiers, she'll definitely take a shot at The Wraith or The Doctor. And The Legion would take one look at The Demogorgon and nope the Frank's Mixtape out.
7. PIG: I know I mentioned The Pig a lot in reference to toxic combos, but this is just about how she would work here. First, she would need double the number of RBTsto account for double survivors. But more importantly is the boxes. By default you have to search at most 4 boxes in (I think) two and a half minutes. This is reasonable (if not easy) on normal sized maps. But double the distance between boxes and this becomes much more luck based. And you can't solve this problem by doubling the number of boxes, because that's double the amount of work for survivors, which makes the problem worse. But if you extend the RBT timer, you take away what little urgency they had. If I had to make a solution, I'd say double boxes and timers, but make the trap activate immediately rather than after a gen. But Pig in general needs some help and I don't want to accidentally anger the Pig mains, so I'll just move on to the next point after saying "devs would need to give The Pig even more attention than she already needs".
8. FREDDY: This isn't a huge deal like it is for The Pig, but my understanding of how the alarm clocks spawn is that it picks the furthest location from you at the moment you fall asleep. This is annoying on regular maps, but would be a giant slog on a XL one.
9. TRAPPER: The Trapper's issue is a pretty simple one: does a double sized map mean double the number of traps? If not, he's going to be F tier in 2v8, and if so, he'll stay the same, but with a potential intensification of his current problem: having to go away from survivors and gens to pick up traps.
10. ENDGAME: Right now, The Hatch (not necessarily keys, that's for another thread) is balanced because when there's 1 survivor left, it's basically a coin flip who finds it first. One killer looking, one survivor looking. But throw in an extra killer and the chances change drastically. So, two hatches? And other issues: 4 exit gates? Hatch(es) open at 2 survivors? Longer EGC? All of this would need careful consideration and balancing.
11. TOTEMS: Totems would just be frustrating. Not only would the 1 in 10 be doubly annoying to find, but imagine one killer getting to 3 Devour Hope tokens while the other camps the totem. This would need more balancing!
MORAL OF THE STORY: 2v8 would take a lot more work than I think most people realize, and while I would love it if they announced that was their next big thing, I also think that the resources that would be needed for 2v8 would be better spent improving things already in the game. Do you want 2v8, or map and killer reworks?