Epubcheck does not support 3.1. And to my knowledge, Kindlegen does not support 3.1 as input, nor does iBooks export 3.1 (could be wrong, though). As to reader-support ... who knows? You can't buy 3.1 epubs to test with. Way too early to worry about supporting 3.1 metadata editing/saving it in my opinion. 3.0.1 was never fully embraced by anyone of any consequence, so I highly doubt the changes in 3.1 are going to bring anyone flocking to it any time soon.
I'm no proponent of zealous spec-compliance that comes at the expense of breaking mainstream relevance. The IDPF declaring which version of EPUB is "standard" has had very little effect on the reality of ebook publishing/editing in the past. How long has 3/3.0.1 been the official recommended "standard" being mostly ignored after all?
Like I said ... maybe an output/input plugin for those who want to experiment with bleeding edge metadata specs?