*is still hoping for a secret Rocket lab/base in Cerulean wherein a new Mewtwo is being cloned*
It's only logical; where did the Rockets in Mt. Moon and Cerulean City run off to? There were a TON of Rockets in that city, they had to have gone somewhere close-by, and Celadon's pretty far off. They could do it pretty easily, too; just include Cerulean Cave and make some kind of hidden switch somewhere on the top floor that leads to an elevator, which goes into the Rocket Lab. Then you go through, fight whoever, and find Mewtwo in a tank, battle it, and capture it. Just for the whole "EVERY LEGENDARY IS OBTAINABLE IN FOURTH-GEN" thing...
Also, maybe something in Celadon; I don't think that the basements that were previously used by Team Rocket should be their base there (those would be turned into something else, like some kind of exclusive shops or something), but there'd be more secret basement floors below those (BF5 and beyond) with some Rockets doing stuff... Though I doubt it. Cerulean's the only real place for them to have a secret hidden base in Kanto...