ATtiny USB data interrupt
This is not remotely going to work.

The upstream side of your hub is not only all but certainly going to be using USB 2.0 High Speed (or even faster) signalling, but is going to have all of the traffic for the downstream devices intermixed together.

Not only would you need a way to tap the 480 megabit stream without electrically disturbing it, you would also need a way to parse and interpret it.  There are debug tools that do this, they are not inexpensive and they use things far more capable than a fifty cent microcontroller.

The only realistic solution to your need is going to be software on the host side.