(Assuming that’s even the case, since their birth was very sitcom-sanitary.)
Vision’s return could obviously be pretty big for the MCU, but perhaps not as big as Wanda’s twin sons Tommy and Billy potentially maintaining their existence upon leaving the WandaVision bubble.
I know that’s a bit silly to speculate after some of what was gone over above, but these two characters – who could eventually have major roles in the MCU’s future – are unique, considering they were born inside the universe.
All I’m saying is that we know altered objects can maintain their bubble properties once exiting this reality, so we should be open to the idea that Wanda’s constructed reality is more real, more meaningful, and possibly more dangerous than we may currently assume.