> By it's very nature these Excel documents will be filled with company data, so I can imagine these companies would also be a bit cautious sending those calculations to the cloud, especially if they can't control the flow of data from their I.T. departments via web applications.

This is exactly what I see when talking to users about xlwings: it needs to run on their end, behind their firewall, in exactly the cloud they have picked (AWS, GCP, Azure).