I wonder how many times I've responded to these Omega Pokémon threads... xD
It's always possible Game Freak could make an "Omega" Pokémon (or "Destroyer", since the classification for Arceus is the "Creator" Pokémon in Japanese versions, I think), but we'll never know for sure until it happens. In the 12th movie, Arceus tried to destroy the world, so it's always possible to view it as both Alpha and Omega, though that may be stretching it. However, Arceus is often considered by fans to be "God-like", so being both Alpha and Omega would make sense in that regard.
Anyway, we can speculate all day about it, but the creation of an "Omega" Pokémon is just something that may or may not happen in time.