There's probably 4 lanes of pcie to connect the nvme ssd to, a couple more lanes to run the thunderbolt controllers, 2-3 usb controllers + a hub to connect the

There's probably 4 lanes of pcie to connect the nvme ssd to, a couple more lanes to run the thunderbolt controllers, 2-3 usb controllers + a hub to connect the keyboard and touchpad, an audio dac and some thermal and power usage monitoring. They might even put the ethernet controller that shoes up on the Mac mini in there.