Not sure how reliable Quora is, but source:
https://www.quora.com/Has-Team-Rocket-ever-stolen-a-Pokemon-successfuly-and-handed-it-over-to-their-boss
It shows that Team rocket does potentially have a skill that can take Pokemon from somebody, whether that is active in this game is yet to be proven.
I didn't see any specifics as to whether we are following Gen II Game mechanics, Gen II Story mechanics, or Gen II All-Inclusive mechanics
We have yet to see any Gen II Legendary Pokemon as well. Only the (assumed) 3 birds and the Mystery Egg, which, based on the current distribution of eggs, could be either Mew, MewTwo, Dratini or the start of Gen II Legendary Pokemon.
How long is this game supposed to go is really the question.
That's an interesting theory.
also, I haven't received an egg, even after losing my poor fishy.