The following contains spoilers for WandaVision episode 5.
The fifth episode of WandaVision has officially dropped on Disney Plus, and with it a whole new slew of questions, Easter eggs, and fan theories. The audience is beginning to realize just how powerful Wanda is, but also that she may not be totally in control of everything that's happening. The show also spent more time with S.W.O.R.D. and what's going on outside of Westview, as after episode 4 it seems that the show will now be splitting its time between Wanda's created reality in Westview and the S.W.O.R.D. agents who are trying to figure out what's going on.
In one scene, Monica Rambeau is devising a plan to get into Westview while being protected, using a vehicle with very complicated tech that, while difficult, would theoretically be possible to create. She then mentions that she knows an aerospace engineer that would be up for a challenge like this. Marvel doesn't usually drop information like this that isn't important in some way, so it's safe to assume that this comment is supposed to be a nod to another major Marvel character. But who exactly is this engineer that Monica is talking about? Here are some of the theories floating around.
James "Rhodey" Rhodes
It is possible that the engineer that Monica is referring to is one that has already been seen in the MCU and is known by fans: Rhodey, aka War Machine. He is one of the few characters already within the universe that would have the skills and tech knowledge necessary to be considered an engineer.
It's possible that in her time working for S.W.O.R.D., before the blip, Monica and Rhodey had met at some point, and are acquaintances. It might make sense for WandaVision to be teasing a hero that fans are already familiar with, because they would be able to bring him in without need of further introduction, and he would already know Wanda and might be able to get through to her.
However, this theory, while possible, is not as likely as another that would hint towards a huge entry into the MCU.
Reed Richards
Perhaps better known as Mister Fantastic, Reed Richards is one of the members of the Fantastic Four, who have yet to appear in the MCU. He's a genius engineer and scientist, and so it makes sense that Monica would think to call him to take on a near-impossible task, and that it's something that she thinks he would totally be on board with.
Another piece of evidence that lends credit to this theory is from a conversation between Monica and Director Hayward in WandaVision episode 4. In this conversation, Hayward is catching Monica up on what she's missed during the blip and says that half of S.W.O.R.D.'s astronaut training program's personnel were lost in the blip. Fans have theorized that this is a reference to the Fantastic Four, who gain their superpowers after exposure to cosmic rays during a mission in space.
Further adding to this theory is a post from an Instagram account created for the character of Flash Thompson from the Spider-Man movies. The post is a picture of a page from the fictional Daily Bugle (run by J. Jonah Jameson), where there is part of a story that reads "put an end to all this 'super' chaos going on! Find these darn astronauts!" It's a very subtle detail, but the fact that it was released so recently, while WandaVision is airing, is perhaps a sign that this missing astronaut story is going to be important to the MCU, and could finally introduce the audience to the new incarnations of the Fantastic Four.
If the astronauts in question are the eventual Fantastic Four team, it lends credence to the theory that Monica is referring to Reed Richards as the engineer that she knows. They would have worked together at S.W.O.R.D., and since her return to the agency is so recent, she may not have learned who exactly the missing astronauts are, and that he is among them.
Marvel has teased that there will be a Fantastic Four movie sometime in the future, set to be directed by Jon Watts, who helmed both Tom Holland Spider-Man movies. It's possible that if this comment from Monica is supposed to be a reference to Richards, fans might see the Fantastic Four pop up in the MCU prior to their movie. These references are a good way to integrate the team into the MCU before their official appearances, so that they feel fully like a part of the world that Marvel has created thus far.
Regardless, Monica's comment was not likely just a throwaway line. Marvel is very intentional about the Easter eggs and references that they put in their movies. It wouldn't be a huge surprise if whoever she was talking about showed up in the MCU very soon, and perhaps even within WandaVision itself.