Well, DC certainly had some kind of gay content in mind for a very long time, after all, that's what he said many times and there are many hints in the game itself. If it doesn't come, it's certainly mainly because of time and missing popularity.
When it comes to Kevin, it's pretty normal that he's boring right now. As most other storyless characters, all he does is serving other stories and quests, while DC obviously didn't bother to include small NSFW teasers (like in Judith's case, for example), for the reasons named above. So it's really not like it would be impossible to make him a more interesting personality.
As Eve's writing proved, it can fit the game pretty well. MC's general easy going and horny attitude certainly helps a lot, so I don't think that a very large buildup would be necessary. It would probably be some kind of bro adventure story with the option for sex at the end. There's really no need for a larger buildup or romance for it to be realistic.
Having said that, it'll always be controversial and this time there's no real way around it, like in Eve's case. But I'm pretty sure they'd manage to write a decent arc for him, too.