IDPF have published EPUB 3.1 spec, but it was about to be rescinded by the EPUB3 Community Group at W3C in favor of a 3.0.2, once EPUB 3.0.2 released, LibreOffice can give support for this.
Steps to Reproduce:
User Profile Reset: No
User-Agent: Mozilla/5.0 (Android 5.1.1; Mobile; rv:58.0) Gecko/58.0 Firefox/58.0
I would wait till epubcheck has a mode to validate this version. Right now it has "20" (2.0.*) and "30" (3.0.*) modes and that's what I followed in libepubgen and LibreOffice UI as well.
Not a bug. Set to enhancement. From comment #1 I understand yes but later. So set status to NEW.
Best regards. JBF