As for what that abundance of rear cameras will do? It ultimately appears to be an evolution of what you saw in PureView devices like the Lumia 1020. The five cameras will work in tandem to capture much more detail than usual, and “10X” the light of other smartphone cameras. This might be your pick if you want a camera-centric phone without spending a small fortune.
As for the public debut? Nokia Anew had rumored an introduction by late January, but that puts it awkwardly between CES earlier that month and Mobile World Congress later in February. It’s entirely possible that Nokia will show off the 9 PureView at one of those two events, when more people are likely to pay attention.