I often think I'd love to engage with some of them.
I know some users choose to add contact details/personal site in their profile, but unfortunately most don't.
Should HN have an option to send a message between its users?
For users who want to be contacted (by pretty much anyone - let's not pretend that HN is some ultra-exclusive club), it's trivial to add contact details to their User.About text - details for platforms they're already on, know & like the features of, etc.
For user who don't, the default is perfect.
For DanG & Co., any "users can contact each other, via HN" feature is a boatload more work. Even if they could just install OpenSourcePackage for that - it'll still need a bunch of hardware infra. Then there's the 1e13 ways in which some users can and will misbehave, via any meaningful chat/message/whatever feature. All of which DanG & Co. would be stuck playing AdminNannyPolice for.