The Molecule Man saved Miles, his family and friends, and integrated them into the 616 universe. What if that included... Ultimate Peter Parker and Jessica Drew?
What if somebody orchestrated the spider biting him
or
What if the spider bit everyone in that lab?
What if Peter was born half-symbiote?
You can tell an original story about a lab accident giving a bunch of people super-powers, and a decent survivor becoming the leader of the good guys.
The main difference in a What If? is that you'd focus on the impact on the Marvel Universe of dozens of new Spider-Man, and the difference for Peter Parker but this doesn't have to be a fanfic.
Sincerely,
Thomas Mets
What if Peter dated Liz or Sally instead of Betty, Gwen, or MJ?
The spider is always on the hunt.
My what if would be Peter & Ben being able to counter Norman and prevent Ben's death in the original Clone Saga.
The city I once knew as home is teetering on the edge of radioactive oblivion