Bluetooth Interference between piconets
I work in a testing facility that particularly tests phones and infotainment systems; there can be up to 20 different piconets running at the same time.

As you said, Bluetooth is incredible at avoiding interference through the frequency hopping spectrum and data whitening, an additional encryption that Bluetooth uses. From what I recall, the data whitening can only be decrypted with the Bluetooth address of the Master device. I do know that the timing of the hopping is determined by this address.

In summary, it will be unlikely that you encounter interference. If you do, perhaps consider building a large Faraday cage :)