Some of the coolest moments from RE6 involved the plot lines crashing together in explosive moments. If Resident Evil 7 keeps the multiple campaigns, we also want it to keep the crossovers. Actually, we want them to happen more often, even if it's just in the form of quick cutscenes. Have characters talk to each other over radio, or see each other from afar, just to keep the connection going.
Some should be full-blown co-op sections, like the boss battles, while others can essentially be set dressing to remind you that the other characters are still off doing their own thing. Either way, it makes the events feel more important, and helps them weave into one massive narrative, instead of a few small ones.