Hello,
After a lot of new tests, this is the final result :
- everything connected to a type-C connector/BUS count for 25% (no matter what the material, even if it's not PCIe device)
As long as plugging something into the port causes the socket PHYs subsystem to send a "hey get ready someone just plugged in" signal to the TB controller it wakes up. Not sure if that happens with a USB 2 only cable also but it might. ( e.g., if the USB 2 pins are active first but then later the device on other side decides to propagate USB 3 then would have to be ready). So pragmatically this turns into "something is plugged in".
Not sure if Apple is going to look at that as a 'bug' or a 'feature' for the software. It isn't presenting active dynamic flow rates. Just potential bandwidth through some low level autonomic like feedback.