If replacing Office / Workspaces is not a monumental task, why are there only two good options? Workspaces is only just becoming a viable replacement for enterprise because pivot tables are hard.
Developing the product itself isn't the reason.
Also, the competing EU-based service might be strong competitors to the ones in the U.S., among people like me who are privacy conscious. I don't use Google services, but I'd be happy to consider using GDPR-compliant services based in Europe.
Libre office is a third option, but does it have much usage? Why or why not?
Could you sustain a development team capable of creating this with a limited market and revenue stream?
This is how promising companies are swallowed by the market leaders.
Market wouldn't be limited and potential revenue streams would be huge. So yeah. Just as a reminder, this is still assuming that there is a significant window where the big options aren't available for Europeans.