LO 6.3 provides PDF-export to PDF/A-2. That's great. Next step would be to implement PDF/A-3. I want to propose this.
Part 3 of the standard, published on October 15, 2012, differs from PDF/A-2 in only one regard: it allows embedding of arbitrary file formats (such as XML, CSV, CAD, word-processing documents, spreadsheet documents, and others) into PDF/A conforming documents.
Adding cc to Thorsten, he added support for PDF/A-2 export
Moving to NEW. I think it makes sense as an enhancement