I would love to see shitposters becoming more careful and creating better posts when they fear for red trust, but I don't have much hope of that happening.
Actually it worked to me. I noticed that my latest posts have been somehow useless, now I am paying more attention to what I am writing. But it would have been if the user get warned before receiving the red trust.
Although I still do not consider my red trust label to be fair.
I do like Ecuamobi's proposal.