I would be opposed to the idea. For one thing, I can imagine that there would be disagreement about which comments were obsolete. Removing some comments from threads but not others can disrupt the flow and leave other readers confused. There have been past discussions on WikiTree about whether old threads should be removed or archived.
Right now, anyone who asks a question can close or hide it, and WikiTree Leaders and G2G Moderators also have that power. I would rather see that done, as Jillaine has suggested, than to have comments or threads removed.