Earlier quoted context omitted.
I wonder if Windows is even their flagship app any more. I think people will give up Windows before they give up Excel. And they might not even notice a different OS, so long as it had the same file manager. In fact Excel is the last non-FOSS app that I still use, even if sporadically.
Give them LibreOffice - Calc and most won't care.
This may be a place where the major paid apps still have an advantage. I think that MS sweats the details of Office the way that Apple sweats the details of the iPhone, and it's laborious work that can only be done by hiring a huge army of programmers and paying them a lot.