It's really cheap to run FOSS on commodity PCs in the twenty first century. Hetzner is very reasonable in the cloud more recently.

It's not a binary switch either, you build the platform bit by bit every year and roll it out to more and more workers. Four dimensional thinking, that could have succeeded already, a decade plus ago.

Sure a few components would have to be written in the meantime. Just a few million a year would be a huge boost to gaps in FOSS.