Where would questions about What-If scenarios go?
StackExchange in general is not the place for these question
I love these questions and, when done well, can be really interesting views into a character or franchise.
However, they're too open ended and too subjective to fit the way our site works.
But with no objective criteria "What If..." scenario questions can't have a single best answer because everyone's answer will be too subjective and only differ in popularity. Then what is 'correct' isn't reflected in either the votes or the acceptance.
Aside †: Wisdom of the Crowd is why we put any weight behind highly upvoted answers, but it falls apart when popularity is involved. The more subjective a question the more swayed by popularity an answer will be.
What can I post?
Besides the explanation in the links above, questions that either request a run down of a character's abilities in general (e.g. What does Storm really bring to the table?) or specific (e.g. How strong is She-Hulk?) are allowed. You can objectively assess both types by completeness and accuracy.
Also, "Has X ever happened..." are sometimes okay when well scoped (restricted to likely scenarios) and well written (some explanation as to why the poster thinks it's likely), e.g. Has Spider-Man ever wielded Mjolnir?.
However, don't fall into the trap of asking "Gorilla vs Shark" type questions, which we have a specific post about explaining how it applies here
Where else can I post?
The specific fandom might have its own forums, or you can look on Reddit for the equivalent. Alternatively Who Would Win, What If Fiction and even AskScienceFiction might scratch your itch. I can't vouch for the quality or speed at which you'll get an answer though.
Once you have enough reputation on the site (which you do), you can come and ask in chat but try not to take over conversations when posing your What If scenarios.
Share and Enjoy!