Hi guys, I like this suggestion and I am sure it will be considered (by both us and our higher-ups), but remember that it's not as everything is as easy as just "doing it now".
Firstly, every new kind of threads needs to be looked upon keeping current rules in consideration. To be specific, current rules allow to have only ONE THREAD SERVING THE SAME PURPOSE opened at once. Adding new tag on items section would make it clear that selling/buying TCs is another "purpose" (which logically is, but for now- technically it isn't). As an effect, every player who is actively using market in every possible way would keep three threads opened on items section: [B], [S] and [TC] instead of just two like it is now: either [B] or [S] (items) or [B] and [S] (tc's). It may not seem like this, but it is MAJOR problem, as even now first page of items (the most visited one) constantly has the same nicks on it, often not letting people who are less active there make their business properly. Adding one more tag for active marketeers would be even more unfavorable for community members who don't trade actively too much- that's why I'm not really for this kind of change.
On the other hand, new suboforum wouldn't have this problem, but having all threads selling TCs dumped in one place could be destructive for TC sellers business (prices war would be really hard)- it would be a problem for both marketeers (they want to sell their TCs with maximum profit, so they don't want TC-USD ratio wars) so as us staff (having TC-USD ratio far from "official" one from torishop is not always what we want).
It just needs a bit of discussion and considering all possibilities, pros, cons and the fact that this kind of decision may backfire whatever we do. Still, it's worth considering so rest assured that we will talk about this, and of course please keep discussing about it as insight of every community member is extremely valuable for us (especially if You analyze this problem from as many points of view as possible).