In a perfect world (my world), following Infinity War, Marvel Studios would have gone with a Richard Rider Nova movie, which would have been followed by The Avengers: Endgame.
Alas, that didn't happen, but the writers on the movie had similar thoughts as they offer up ideas they had put together for the two movies, which also includes House of M.
Speaking with THR, Christopher Markus and Stephen McFeely reveal they had been tasked with coming up with every possible idea for the two films, which came together in a 60-page document.
Nova in Infinity War and Avengers: Endgame
Regarding Nova, he would have taken the place of Silver Surfer from the Infinity Gauntlet comic and would have been used instead of Hulk for Infinity War in the Sanctum Sanctorum scene:
I remember going through several scenarios of Nova. Thanos could come and kill all the Nova Corps, except one guy. Richard Rider, who then becomes … I think in that scenario he became the herald, kind of like the Hulk was [in Infinity War when he crashed into the Sanctum Sanctorum].
The final version of Infinity War saw mention that Thanos and the Black order did decimate the homeworld of the Nova Corps, Xandar, so we see, as many fans have speculated, that Infinity War could have introduced Nova, who eventually could have been a part of Avengers: Endgame. It would have been really cool to see that happen, and if it did happen, I wonder what would have become of the Hulk? While Richard Rider Nova didn't end up appearing, at least Marvel is talking about the possibility.
House of M in the MCU
In the comics, House of M is a big X-Men event that sees Scarlet Witch having a breakdown and altering reality which sees her erase mutant powers from existence. Regarding their ideas for the movies, Markus and McFeely admit it would have been hard to do as they changed Scarlet Witch in the MCU so much:
McFeely: I think House of M would be awesome. But you've got to earn it.
McFeely: It might take awhile. And it seems hard.
Markus: It doesn't really seem within her [Scarlet Witch's] skillset.
McFeely: We took her skillset away. She had mind control stuff early.
The article also states that since McFeely and Markus came up with the idea prior to the Disney-Fox deal going through, that the storyline would obviously have to have been tweaked to accommodate the X-Men characters not being a part of the MCU. We can probably guess that the MCU version saw the Avengers deal with Scarlet Witch changing reality, and even using different versions of the Avengers, as the House of M reality replaced the Marvel 616 reality.