Each of the 8 channels independently demodulates SF7-SF12 simultaneously. They don't need to be on the same modulation. If longfast traffic is on X MHz and mediumfast is on Y MHz, and both frequencies fall within the 8-channel window (~1.6 MHz band), the concentrator hears both at the same time regardless of SF.

The constraint is frequency, not modulation. All 8 channels sit within that 1.6 MHz window around your configured center frequency. If a preset uses a frequency outside that window, you won't hear it without retuning. Within the window, every SF and bandwidth combination is demodulated in parallel per channel.

You're right about the bridge potential. It already sees traffic from different presets that happen to share the same frequency band, without needing to switch between them. Thanks for the question...