VPK content could indeed be something that workshop map authors could stipulate as a required separate download. 5 maps that contain all of a pack's assets would actually be stored on a client's machine ten times, because of the current dual locations.
Though, does each map that uses the Construction Pack, for example, use every asset? How likely is it that a user will have multiple maps on his machine that use the same content? Given that a VPK would contain all of the assets, and would not be compressed, would the benefit of separate content be negated by its uncommon usage and the new BSP compression?
Adding support for content packs on the workshop would wrap up contribution credit very nicely. I think it should also be possible to add to existing VPKs on a client's machine, rather than have to add new ones. But I would not want to encourage the creation and necessary download of large content VPKs where only a couple of assets are used by a handful of maps.
The other thing is it's a good opportunity to reorganize the way subdomains are handled and listed. For instance we could really use a list of what TF2M (and maybe others, like BulletCrops) have put out somewhere. For example, I found Fubar's map release thing and have no idea how to get there again. I'm not sure how new people are supposed to find the construction pack or past contests without knowing where they are already.
I agree. I had trouble finding existing content packs, and had to search for them on Google. The main web site doesn't acknowledge their existence in any significant way, but it should be pushing them in to people's faces as it's a unique selling-point.
Coffee, I had this on a list of thoughts about TF2maps, but I think you should take it to the site suggestions forum!