Although GPON is shared, it is not half duplex! I'm not exactly sure why the asymmetrical version won out, perhaps due to cheaper optics back in the day?
Latest iterations (NG-PON2 and XGS-PON) are 10G symmetrical, and XGS-PON is now cheap enough that GPON doesn't make much sense. AT&T Fiber in the US has been deploying it for the last few years.
Yes, the different bands are not collected at the same time across the whole scene, so you get ghosting with moving objects. The SkySat sensor [1] is split in two halves: panchromatic and RGBN (where N is near-infrared). It takes lots of captures as the satellite travels that are later aligned and combined into one version.
