Well...VC glitch Mew could be shiny were it to have the right IVs, but you cannot legitimately send one of these over to gen 7. There was a Mew event for the VC which can be put in Poké Bank, but, AFAICR, due to how these events work, all of its IVs were preset, and they used that to make sure it couldn't be shiny when transferred.
To this date, the only legitimately possible shiny Mews are those caught in Faraway Island (Emerald), which can only come from japanese games.