Comment by gggggggoodlord

In regards to your first point, I'm actively testing conversion scenarios of .xlsx to .ods (ODF 1.3) with LibreOffice, and depending on what you consider significant properties there's definitely some loss along the way that might hurt. Mostly looking into diagrams at the moment, and some break under conversion (histograms and pareto for example), while others aren't displayed properly (stock charts).