I too am interested in a similar feature, but it doesn't have to be a wordpress integration. I'm interested in having the ability to use an existing user database and add flarum as an extension, so to speak, to my existing site, but only have a single log in process. Once the user is logged in to my site, they can freely use the forums like they can the rest of the site.
I'm not planning an MVP that includes forums, so I have some time, but I would like to have this sooner rather than later.