I would actually be on board with that, if the boot/firmware (micro)SD was separate from the main OS drive, because the annoying thing about the Pi is that it can't take generic images - you have to flash a pi-specific image to your card because it has to include the firmware. There's a part of me that says by the time you've put the boot firmware on a dedicated card and made that card robust enough to survive the lifetime of the machine you've just reinvented built-in flash chips, but I agree that the ability to trivially remove it and have all the (changable) firmware in one card is an improvement over the status quo.