I've thought about suggesting this a couple times before, but like they said above I don't think there's a big enough audience for it here to warrant one, it probably wouldn't be used that much. As it stands the Creative Media Showcase thread doesn't get used often at all, so a sub-forum probably wouldn't be viable...
However, I do like the idea. One thing that has always bugged me about the Showcase thread is the lack of people commenting/critiquing other people's work and instead just ignoring the other posts to share their own stuff, so perhaps a section/sub-forum would help encourage this kind of discussion and therefore make people want to post their work more often as they know it'll likely be evaluated by someone? Also as shown above it seems that not everyone is aware of where this kind of work should be posted (even half the posts in the Showcase thread had to be moved there from other places since people didn't know where to post their work), so perhaps if there was a distinct section for it then people would realise it's there and become more interested? That is a completely hypothetical assumption of course and is a bold comment to make, but I'd wager money that it'd turn out to be true.
If it was implemented, the section could host a lot of threads to get less musical members involved such as karaoke, how-to videos (eg people upload lessons of how to play certain songs or instruments for other members to use), lyrics writing, group projects, etc, and the amount of different competitions that the section could run is staggering, so I think it certainly would be an easy area to keep fresh and active if it had the right amount of interest. It'd most likely be a slow-starting section whilst people get to grips with what they can post there and actually get round to making the work to post, but I feel like it could most likely grow quite large given the right members using it.
As a side note, I have seen quite a few people around the forum that record/produce music (original and covers) that have sent work to other members in VM/etc to be commented on, so I don't think the proposal is completely off. It depends on whether they'd actually use a section for it I guess. Personally I too have been looking to post some of my own work to get critiqued, but since the Showcase thread rarely ever brings comments I've posted it on other sites instead, and I expect I'm not alone in this.
If only we could trial sections for a few weeks haha.