My idea is not to just change icon for a category but for each forum, as you choose a description.

You can see an example on the screenshot.

I believe it will improve the clicks conversion of users.

If i understand you, you meaning different icons for each category topic, for example: http://www.jpeg.cz/images/2016/12/13/kAXIp.png IPB each game has different icons. If you mean this i'm totally UP for this idea, it must be good for a sport, games forums etc.

Maybe it's signs on performance of website, we will see ;).

I have found how to change the fontawesome icon (on the left of each forum titles) globally with this : http://docs.layerswp.com/doc/how-to-replace-font-awesome-icons-with-css/

But i think we can't change only one icon specific to a forum.

The goal will be to have a different icon to each forums created.

Is there a way to obtain this ? Or could it be an option for a next update ?

Thank you for your response