I want to keep the forum messages but instead of posting only messages I want the user to be able to post a product that he wants to build (think Product Hunt).
Essentially it would be a form rather than a simple message. In that form the user can post a video, a picture, different descriptions etc...

How do I do this ? Do I build a widget, a plugin ? or did somebody already built this for Nodebb ?

@julian happy to share what we came up following your directions and share plugins and code with the community.
Let us know if this is of interest.