To me tags have always been more about the theme of a post rather than what form the content takes, and it seems natural to interpret them thus. So your idea makes a lot of sense to me. Keep the tags in addition to sorting by content type (video, music, link, essay, etc).

Sounds simple, but the main problem is how to enforce the separation of content. You can't just slap on a video section, and then have people submitting written stories there instead of videos. To be effective, the site's UI should naturally limit content to the appropriate type. For example, to submit a link you would paste the link into a form, and maybe fill out another box on the form that allows, say, 255 characters to describe your link. And that's it. These restrictions would also have to be enforced at the level of the blockchain API, to prevent bots from bypassing the rules. Not sure if the structure of the blockchain itself would need to be changed, probably not as long as the APIs are the only onboarding point for content, and there was some schema for interpreting data properly when it's read off the blockchain.

This would go a long way toward improving Steemit. To some extent my carefully cultivated feed acts as a nice strainer to pluck out the meat I like, but it's a lot of work sifting through stuff in the first place to find the right people to follow, and it's not perfect (especially with all the random stuff that gets resteemed these days).