The revelation will be very important because DPC is keeping this door closed to us. The reactions of Maya and the MC alone suggest that. Why would Maya be startled and the MC practically freeze if it's only of minor significance?
We should also consider the ending of Episode 3.
"Doors are funny."
"Be it metal or be it wood, they’re made to do the same things."
"To keep you safe or secluded…"
"...and to protect the things you value."
"Protect you from whatever is on the other side."
"Or worse…"
"They are made to keep things on the inside."
"Things you don’t want anyone else to see."
"Locked away."
"It’s weird to think that something so simple as a knock, often repeated three times, is all it takes to get someone to open that door."
"Curiosity takes over and it exposes you."
"Some doors are meant to stay closed."
"Because opening them…"
…
"...may change everything."
These clues alone suggest that this door is important not only to Isabella, but also to the MC, even if he isn't on Isabella's branch. I can only repeat myself. We learn from Jill in Episode 5 that this is why the door wasn't locked before. Isabella has known who the MC is since Episode 2 and only locked the door for that reason.
