New gamemode "deathmatch"
It looks like its not the first 2v8 gamemode which lacks of survivor players, new gamemode might solve this. You could expand maps a little more (or keep the same) and lets say it would be 12 survivors and 2 killers. The "deatmatch" will be timed (10 min) and the side that will get most points will win (of course remove hook stages). Such points can be earned by literally any action performed by killers or survs. I understand that this idea will require a lot of math from you (developers) to calculate fair amount for each side for possibility to win, but you have good working brains and I believe in yours skills! Regarding generators on this gamemode they will be infinite, but if generator will be completed it will be blocked for 45 secs for example, and upon opening it will reset of course. Such gamemode will bring ability to bring more survivors into the room without making it overwhelming for killer side to fight against a bunch of players. I hope I gave you an idea to think about good way to make killers wait a little less for new match!