Surprised the sharp-edged oscillator signal was not degraded over that distance
I don't remember having measured a signal transmitted like that, but I won't expect it to be completely deformed, especially with a twisted ground wire coming with it.
Anyway, all the harmonics of the signal are not necessary, as the chips generally have an input stage that would reconstruct it, so it is not a problem if the signal is a little degraded (not too much though, and it depends how it is affected).
..... or maybe it was as they discontinued that item.
It seems to be still sold in some of their kits.
So, is the I2C signal broadcast simultaneously to more than one camera or do you have to send to each camera in turn ?
I²C is a bus of communication. This means that there can be multiple devices on it.
For that, there is some minimalist hardware parts (inside chips) and moreover a protocol which says which one is allowed to speak on the wires.
This protocol uses addresses to determine it (orchestrated by a master), thus there should not be two devices with the same address on the bus. For example, the EEPROM and the camera modules are connected to it.
But, their addresses are not modifiable, so there must be two buses to use two cameras.
The CAMArray boards of Arducam apparently have a CPLD which likely decode the I²C signal coming from the raspberry and transmit it to each camera separately (and perhaps does some treatment in between), making the raspberry think there is only one camera. The CPLD also probably get the image from the CSI lines and mix the images to return only one CSI signal to the raspberry.
I do not know the product, but it is what I can infer.