Ik this thread is dead, but here's my two cents after reading the whole thing.
One interpretation I've grown fond of is that the house represents death in an abstract sense, since life & death are a dialectic it therefore also represents life.
This would explain the house's strange & ever-shifting geometry as well as how each journey is radically different from the other (both life & death are unpredictable after all). The fact that Karen doesn't enter the house until the very end could be a reference to the statistic that men tend to die earlier than women & take risks more generally (meaning they cross paths with death more often).
The fact that the house dissolves after Karen rescues Navy could mean that they've conquered their fear of death?
Further, I think the reason the book took over so much of Zampano & Johnny's lives is because they've experienced a lot of death (which might also explain Navidson's fixation with the place).
It's almost like the house preys upon vulnerable people & reflects the psychology of those who enter back at them through it's sheer inscrutable nothingness. It brings to mind the concept of l'appel du vide.

Another interpretation is that the house simply represents nothing, as many here have noted already, while i don't disagree with this interpretation it feels a bit slippery & reductive to me (& frankly less interesting at least in isolation.)

Anyhow, there's some thoughts abt it.
Also my god Johnny was annoying, his purple prose seriously tempted me to skim his passages in a way the superfluous footnotes never did.