I suppose there is some value to this as a thought experiment but pretty much every tier in that architecture has breaking flaws. The most relevant being that anything that has an audience of 1 million users cannot run on an architecture that has single points of failure.
Physically the hardware can't handle it or are you just advocating that it shouldn't?
Hardware fails. This architecture has single points of failures which means if one of those instances fails the entire system goes down. This is generally not acceptable for environments with 1 million active users (which implies high business value)