I would like to see a messenger app like the one Facebook

I have good news on that: There is one in development by Hive account@therealwolf. I haven't tested it yet, but I think it's the closest to what you are looking for.

What I like about Steemit generally is that there might be a lot of things missing, but what is much better than in other places is the simplicity of the design. It's reduced to the minimum and anything else is left to developers to find solutions for - and they develop like hell. This is a very intriguing and different approach. Especially for programmers (like not me) this adds a lot of value to using and spreading the site.

On the feed topics, I'm missing that as well. I never go to the trending section, I rather pick interesting users and then look at my feed. Perhaps, someone could create bots that automatically resteem certain tags (or better a combination of two or three) and then you just have to follow these bots and get interesting stuff delivered into your feed.