If the content were organized by type, then the submission editor could serve a gatekeeper function in terms of requiring a video in the video category or limiting the number of characters in a post, etc. Yes, it would be fine to have mixed content and overlap for certain categories. What you're suggesting might require more intensive curation within categories or tags. I am not against this, but it is a big job, so we need to think about how the market would incentivize that that sort of gruntwork also.