A fresh look at the kernel's device model

My most recent use of buses is an PCIe-connected FPGA's memory map exposing various pieces of functionality, so a new fpga bus was created where subdrivers are matched to ranges of the FPGA's memory map. Here too, each subdevice is addressible within the bus by using the starting address.

Probably in the workqueue example as well is i2c/spi/pci/... devices attached to a bus are enumerated in a particular way, which implies they are somehow individually addressable within the bus context.

Classes, as you mention, group devices by common functionality, instead.

But you have clearly identified that there are many other uses... Apparently they're just tools in the driver writer's toolbox...