FWIW, current releases of LibreOffice 6 can open and edit documents from SharePoint document libraries. Also, I have not had trouble opening OOXML files (.docx

FWIW, current releases of LibreOffice 6 can open and edit documents from SharePoint document libraries. Also, I have not had trouble opening OOXML files (.docx, .xlsx) in LibreOffice. The main problem with LibreOffice, from my point of view, is that there are many third-party applications that expect MS Office to be installed or use it exclusively for data import/export. For example, Autodesk Inventor can create a bi-directional link to Excel and export the list of parts of a model to Excel; ePlan, too. Our PDM system comes with an Outlook plugin that allows users to upload emails. Our ERP system can export stuff to Excel, but not to LibreOffice. The list goes on and on. For a large number of use cases, LibreOffice is perfectly cromulent as it is. But as long as all those third-party application rely on MS Office, it will remain dominant, regardless of the price or technical merits.