It's been around for awhile, Jason Santa Maria probably did it most famously with his blog way back when and more recent CMSs like Visual Idiot's "Anchor" were

It's been around for awhile, Jason Santa Maria probably did it most famously with his blog way back when and more recent CMSs like Visual Idiot's "Anchor" were intentionally created to allow people the ability to design for the post, rather than the site.