"PokeBank has been released onto the world, although over a month after it was originally scheduled to, and users are quickly finding problems with the software, and the way the whole process works in general. In this episode of NE Radio, Elia goes on an extensive PokeBank rant, complaining about UI issues, as well as making several suggestions for future updates to the software" -- Nintendo Enthusiast.
Outside of Pokemon Go, Shiny Celebi will become unobtainable when Pokemon Bank closes - until that happens, here's how to get one.
Shiny Celebi was available via movie promotion event. Dexoys is the only one you gotta worry about shiny because it can on be shiny in original gen 3 carts. That being said, they arent closing bank down. This was already stated multiple times.
Shiny Deoxys is currently exclusive to Generation 3, which means it'll become unobtainable once Pokemon Bank closes.
Pokemon Bank is presumably closing soon, and several Shiny Pokemon will become completely unobtainable afterward.