Disclaimer: I don't read Spiderman comics, and I eventually lost interest in the movies. I'm also not particularly gay myself. Disagreeing opinions and statements are welcome.
I wouldn't like a new Spiderman incarnation that is just like the previous ones, just with Martin John instead of Mary Jane. It'd be very obvious pandering, but not bring anything new into it. Gay people are not defined by being gay, but are (and in case of comic book characters, should be) well rounded, multifaceted personalities. In short, only making him gay is boring. Which is what askold said.
I want to see something new and radical. Let Peter live on a space habitat. He isn't bitten by a magic spider, but develops a fascination with the evolved-for-zero-gravity spiderites that live in the station machinery. He equips himself with homemade augs and biomods, and takes up the good fight against the criminal underbelly, against corrupt habitat-nation officials, against external threats, against his personal troubles. Oh, and his eventual love interest is another man, too. Or, what the hell, a fugitive genderless AI that fled into a mobile android platform.
I'd read that.