That is actually a great idea. It's a pain currently trying to browse and to find the most helpful answer on the thread in the sea of shitposts.
if such function existed, it would be possible to just skip all the unhelpful answers and then read only the best answer.
The idea is good but the problem is the low number of merit sources at the moment and also the low number of threads that they patrol on. I believe if there was an option offered to the thread maker that "allow searching posts by top merits" when the thread would be active it would be a good thing to segregate the shitposts from quality posts.
However we need more exposure of threads from merit sources then.
O don't think merit sources are the problem. If there is only one merited answer it will be on top, and any user can merit.
Maybe we need more merit sources, (for sure better distribution, as many local boards don't have any) but this can be implemented anyway.