itlo I mentioned the social media platforms like Facebook or Tumbls as examples how they got big, and not as examples for the needs of a modern forum.
That does not make sense. The point of making feature requests is for the needs of a basic forum set up. I was agreeing with your feature request, but not the source of why. Either through "getting big" or otherwise, it's not safe to entirely rely on social media platforms as the sole proof (that you did above).
My suggestion was to relate anything to a discussion platform, as I did by invoking the concept of blogs (a type of discussion paradigm) instead of social media (solely for networking individuals and not solely for discussion). "Getting big" is not a valid reason. the sole purpose of bringing this up is to make sure the aims for flarum don't veer too far to another concept (social media). It's okay to borrow concepts from social media. But please keep it within hard focus of a discussion platform. For example, using Twitter's mentions within the scope of tagging users to join a discussion is a great example of borrowing social media concepts for a discussion platform. I don't think "because it made Twitter popular" was the reason it was put into Flarum.
My message above is aimed to everyone in general, not completely onto you, @itlo.
itlo Or the Twitter hashtag stream https://twitter.com/hashtag/Obama?src=hash (but here should be considered only the tweets with thumbnail and not those with full width pics or vids). In all these examples the emphasis is on the topic (or tweet, or question) with all it's aspects (title, text body, user and media), and these are what we need from a forum application too.
I agree with you assessment on how it can be applied to a discussion platform. I have also mentioned #hashtags to the Discourse devs for topics to be linked organically within the text. Clicking a #hashtag link would pull up a search for it to show other instances where the hashtag was also typed.
itlo (look at discourse frontpage...terrible)
You should break down what exact elements you don't like with Discourse's method of showing their topic lists. Also, there really is no such thing as a "front page" for Discourse. A forum owner has the option to use a "latest" feed or a category listing for the index. You need to be more specific.
itlo When I visit a forum for me is important what the topic is about and its content, not the number of views and replies.
I disagree because those number of views and replies show interest in the topic itself. The metrics aren't just "interesting" but they are useful too, if one understands why they are there in the first place.
However, back to topic thumbnails.
The biggest reason for using topic thumbnails is for added clarity and context. A perfect example is a topic that asks "what is this?". They post a picture of an object. Without the image all users see is "What is this?" for the topic title. It gives no context as to exactly "what" someone is trying to identify.
That makes thumbnails useful and not simply as eye-catching objects for the sake of having it.
I have noticed flarum already uses the concept I was mentioning earlier, about placing the user's avatar at the top of the topic thumbnail.
See the smaller pin icon? I can possibly see the topic thumbnail in place of the avatar, but have the avatar as an icon placed similar as the pin icon, on one of the thumbnail's corners.
That way flarum's current ui "logic" is used to its full potential and not overwritten just for the sake of having topic thumbnails.