Interesting because I'm building ooxml-cli right now, for editing pptx, docx, xlsx. At work I had to adapt a pptx to a corporate template and tried via agent. It kept failing so I started building and then it was able to relatively quick and accurate do what I needed. Then I needed it to make tables, add pictures. Recently wanted to get data from an xslx and replace text in a presentation etc.

So the tool is growing and maybe this would be interesting to have as the non LibreOffice dependent viewer...