If I recall, Yu-Gi-Oh! ARC-V used a special opening to celebrate the YGO franchise's 777th episode, which included clips and visuals from all of its predecessor series. The song was still the same as usual though, haha.
I suppose Pokémon COULD do something simple like that for its 1000th episode, but then again, the overall episode count seems pretty bewildering if we consider all of the special/cancelled episodes, and I don't even know if there's an official numbering (or even a universally accepted consensus) that accounts for each series in the entire franchise.