Direct messages: No issue for this. The idea here is 1 sat per message, paid to the receiver, which also prevents spam (and no free DMs).
Post tags: No issue for this. This would be an alternative to subreddit-like grouping of links, more similar to lobste.rs where everything is still easily found on one page. There have been a few discussions on SN about this (but are hard to find because no search or tags).
Here are my wants (somewhat prioritized by what would likely be quick to implement first):