I'm dubious about this in principle, but even if we accept for a moment that notifications are an appropriate solution, the example provided is terrible because it's so vague, particularly when you realise that an ExpressCard can appear to the kernel as USB, so the user's experience is "I plugged in my FooBaz card, and Linux said I'd connected a USB device - but the FooBaz is a modem not a USB device".
If someone's excited about notifications for USB devices, let them first go solve the case that's agreed to be a problem, which is when a user plugs in their USB Foobaz, and Linux doesn't have a suitable driver. udev (with perhaps a small tweak to the kernel) can figure out that nothing uses this device and /that/ is worth telling the user about. "Vender Inc Foobaz connected but you don't have a driver for it [Don't show me this again]".
Once /that/ works, it is extensible in a good way ("Connected device needs firmware file FooBaz-1.28.bin. Please install firmware and re-connect" and "The FooBaz webcam you've connected has an unsupported Baz controller") which tell a technical user what they need to know, and provide the non-technical user something useful to report to their tech support.