I personally don't have any issue with multiple items in one thread if the formatting is good and the thread title is proper.Is there an option to give multiple trader ratings/feedback for 1 thread. I think most people are motivated to open more than 1 thread for the ratings. Also the argument of clutter can be given by the seller as well. Too many things for sale in a single thread can cause clutter and look as a nuisance to the thread viewer as well. Personally, I am less motivated to open a thread which has too many items for sale and prefer single item, single thread approach.
I don't know about the feedback (and tbh I don't care much about it either), I don't leave feedback unless sellers ask me to. So my feedback is still single digit. But I feel that if seller/buyer wants multiple feedback for a single deal then that's unethical.