I hope that unmerited post won't be hidden. That will limit the breadth of the thread considerably.
If it is to be done, then please make it user selectable.
I don't think it could be implemented without being user selectable. All posts have no merit when they are first posted and if they were hidden then nobody would be able to see them to give merit and unhide them. The way I interpreted the suggestion was as an optional summary view to be used when a thread is too long and you just want to skim through and find the important bits.