In my opinion this will just cause even more questions and confusion among the players, not to mention people asking ''why can't i use the trade chat'' in adition on ''why can't i trade?'' If that for example is implemented, it wouldn't affect only the trade channel but the whole chat overall. People need a picture how much something costs and some do like to get some pokes ready in advance or simply do private price checks. I personaly didn't encounter that many trolls/spam accounts that it would require a restriction for a badge based permission to use the channel. Maybe the idea has some potential but I don't see it being urgent.
its not urgent tho .. just a suggestion if staffs like it , you might be right of what you say it can result on spam on the whole chats yeah true .