New Theory: SWORD (or Hayward) was actually working with Wanda to resurrect Vision (since one of their new mission parameters is AI) but off-book, and came to think that Agatha Harkness (or magic) could be the one missing ingredient to making it happen. Agatha helps, but unbeknownst to Wanda, calls upon Mephisto's power to do it... but in exchange for the children - beings from an impossible coupling that should never be able to exist. The sitcom world being the way to help integrate Vision back into life but also provide the children for Mephisto.
Well, that's one thought...