I run a personal Pixelfed instance as well as a kbin one. I think the "easiest" or most sustainable would be if there was a pixelfed instance also stood up at the same time a new kbin instance is started which had some kind of SSO for the kbin and pixelfed instance.
The challenges I see with this:
Media storage space for a place like Kbin.social could grow pretty fast, especially if people really started uploading videos.
Bandwidth concerns may or may not be an issue, but certainly would need to be carefully considered.
Moderating the pixelfed side could be a lot of work, especially if people start only using the pixelfed site and not posting anything to kbin. It becomes like Imgur and moderating images, especially when people are uploading non-OC constantly, adds greatly to the work-load.
I've done a little testing to see how embedding/linking to images on a pixelfed instance would work (without any special integration) and it works.