I keep hearing the comment that the general public would be interested in Khan. I plan on asking a few people I know that are vaguely familiar with Trek on their opinion instead of just assuming what they want to see. It's hardly a representative sampling, but it's a lot better than the guesses I see here.
I started by asking my wife, who isn't very Trek-knowledgeable about what she thought the next movie should be about and the conversation went something like this:
Me: What do you think the next Trek movie should be about?
Her: Does it have to be about the original series?
Me: Yes, the same crew in that time period.
Her: Uh, how about Tribbles?
Me: How do you make a movie about Tribbles?
Her: Ok, then Klingons.
Me: Well, some say the Klingons have been done a lot.
Her: How about Data? Is he around in this time period?
Me: ...no... There's a lot of speculation that the movie will be about Khan.
Her: Oh, the guy played by Charlton Heston?
Me: ...
Her: Shouldn't they do something different?
The Data and Heston comments had me particularly wowed, but this might be what to expect from an average moviegoer. They might not really care who the villain is. Star Trek isn't Batman or X-Men.
I plan on asking several more people just to get a well rounded group of opinions.
I think some people are confusing the reuse of the Khan character for the reuse of a Khan story, which is not what the writers have indicated they desire to do.
The thing is, how much different could the story really be? Khan is a really two dimensional character that was only made classic by Montalban and the directing. There aren't infinite realms of storytelling with a guy who wakes up and wants to take over, especially as it relates to the Enterprise crew.