I've had exchange ads in the past. I no longer do for a couple of reasons. The marketplace doesn't have the social proof of the forums. It is way more anonymous, which makes it a low trust environment. That also empowers people to submit lowball offers, which is all I ever received to my marketplace ads. When I've exchanged with people through the forums offers have consistently been fair to both sides, or at least in the ballpark.
Also, I don't think the search really works, because it requires too much specificity. As an example, I posted an Oahu unit week 52 with a request for worldmark points. However, someone else posted a worldmark unit (at a specific worldmark resort) which didn't match to my search. I'm not likely to put all 60+ worldmark resorts into my search, even though someone could list under any of them.
Anyway, your ball of course, but I think the marketplace has structural deficiencies that make it unsuitable for exchanging that an exchanging forum would address. It isn't a good use of my time to craft multiple exchange ads for a system that doesn't work, so I don't.
I would need many ads: one to offer my Oahu units, one for sheraton desert oasis, plus multiple ads for worldmark and shell. And that would be just on the offering side. I could spend hours putting up ads and have a low probability of a match. With a forum I would put something like:
W: XXXXXX H: SDO, Worldmark, Shell, Oahu
(Xxxx being what I wanted, which is redacted to follow the rules)