It should come as no surprise that many people read hentai as a form of idealized escapism fantasy/porn. And while many people use this outlet for fantastical reality-bending characters, art, and porn, some of us enjoy, (from time to time), a great love story that comes complete with visceral vindication.
A few of my personal tastes are things like dark skin or whatever, but I personally love stories that utilize or work towards marriage/long term relationships. My personal favorite in this regard, on this site, is "Yanagida-kun to Mizuno-san."
And while I certainly don't mind crawling through mountains of good hentai to find that perfect one, I wouldn't mind seeing a tab for marriage-related H-manga.
Is this a good idea, or should it stay a sub-genre remaining in the "Vanilla" tab?
Not many manga (at least, original series ones) get that far since the characters tend to be either young, or the series isn't long enough to detail the length of a lasting relationship.
It would be tough to go through all manga and look for such tag indications: if there is no scene showing marriage, it would require taggers (and non-translating uploaders) to go through all the text of each manga to check and see if any character mentions marriage...