Being able to see the list of those who viewed your thread.
It won't work, because many people use more than one account, and a lot of users read many topics while being logged out. Which is why their "online time" can be sometimes measured in single days or sometimes even hours, even if they have hundreds of posts. Ideally, posting without logging in would be possible, just by signing some message, and broadcasting it through some channel, but we are not there yet, on our centralized forum (but such systems could be prepared independently, and could use the forum engine as a proxy, to publish some content).
Hi, I noticed you viewed my topic, but didn't engage. Why?
I got that kind of messages. Well, what can I say: welcome to the Open Source world, where people demand from you more, and donate you less, than any company, which would hire you to write any closed source code. It is normal to receive PMs like that, after a while you will get used to it, if you will post something worth reading, and some people will want you to post more, or explain some things in more details. I had some PM conversations with some people, which could be just included in normal topics, as regular posts instead, and then at least they would be indexed by search engines, but it is another story.
Also, when more people expect more things for free, it is good to start a fresh account anyway, and climb again from Newbie to Legendary. It is healthy to break contact with some people, and publish some things from a new account, to see, if good posts are merited, or if it is still content-based, as it should be.
Second, because it could easily be bypassed it simply by opening your post in an incognito tab without being logged into the forum.
This is the default way of reading content for me, and it should be promoted in more places. I hate when I need to use proxy pages, to read Twitter posts, made by some developers, without logging in. It would be better, if they could be accessed directly, also because it would be much easier to archive some good ones by any web crawler, to find them easier next time, through any search engine. Which is also why I hate the fact, that some Polish forum was taken down, just like that, and invalidated a lot of previously working links, including posts, made by early adopters from 2011, only because the current community want to use Discord instead:
https://forum.bitcoin.pl/Do you like cookies on websites?
No, and I want to see them removed from the case:
https://www.youtube.com/watch?v=TzoW_GO45vk