I've been struggling with this and I've posted before and the solution was to run a script and a plugin to have all users Ignore a category. That causes a whole other set of issues.
The situation is that we have categories that are very noisy and of very low value to anybody but the (usually only 2) participants. For these categories I would like the following "Quiet Mode":
Topics do not appear in All Unread, All Recent, nor All Popular
Topics do not appear in Suggested Topics nor any other widget list
Topics do not appear in the email digest
Topics would not be considered "Ignored" so they would still show up in pick lists so that you can filter on them.
If you're good with this, I can file something in Github. I wanted to post here first before.