It occurs to me that you can send a 9gb signal and a 1gb signal over the same optical fiber, on the same wavelength, at the same time.

You just need your 10gb receiver to contain a 1gb scrambler, and before sending a symbol at 1gb, you first send it at 10gb so all of your 10gb receivers can filter the 1gb noise out of their signal, then you just merge both signals together.

The only thing you need in your 1gb kit is an attenuator so that the receiver doesn't register the 10gb signal as a "light source always on" status...