I haven't seen any of this, not in a slash veine at least. It has turned up in a threesome incarnation with T'Pol, but I haven't see it be just them. A fic entirely centered around them without involving T'Pol, romantically. What do you guys think? Why isn't this seen more?
I have a story in the works featuring this pair, it also features a Hoshi/T'Pol relationship in the backround. Personally since Koss wasn't fleshed out as well as some characters like the ones we normally see being pair with Trip, I figure he is just as slashable. At least in an AU context, that is. It's very hard to make their relationship completely cannon, like with other pairings.
I've chosen to maintain the bond between Trip and T'Pol. Untilizing the idea that mating bonds aren't the only kind which can be spontaneos. In theory a family or 'sibling' bond could form under the right circumstances, in any instance, I have yet to see sudden family bonds in ENT stories. And I've yet to see it in adults in any Star Trek fandom at all.