Ok I guess I’ll be more specific:
Someone already beat you to it.
But hey, sure, I’ll bite on this “idea” of yours.
How do you intend to actually do this?
What engine will you use?
Are you planning on unifying the two VERY different art styles together by creating your own style, or will you just be stealing existing sprite work?
Do you actually know how difficult it is to make a fighting game?
Who is your target audience?
How do you intend this game to play?
Are you planning on focusing the game play more on the SF side or the MK side?
How do you intend to handle the HUGE tone disparity (MK’s fairly serious and extremely violent tone vs. SF’s more light-hearted and cartoony tone)?
I’m fairly certain you can’t answer any of these questions, but even if you can, you’re here asking other people to come up with ideas for you. I’m just waiting for the post where you start looking for people to create art and program for you as well.
But hey, let’s just go ahead and assume you actually can follow through with this on your own.
Does anyone actually want this game?
Well, the posts above should give you a pretty good idea on that, but seriously: if Capcom actually thought this was a good idea, they would have done it years ago ESPECIALLY if it was going to make them more money. Capcom likes money.