I think it's nice to see. It means the spec is probably pretty close to being finalized, because in order for that to happen, there needs to be at least two browser implementations.
The only reason I marked it as "supported" is that it's "supported" like like any other purely semantic tag is (e.g. <nav>) It's just in with the forms stuff because it's specifically for content coming out of form calculations. I didn't even test the "for" attribute stuff, but wouldn't be surprised if that's not supported.