Thank you!
XLSX and ODS support won't be trivial, but I see the value of having it. I added it to the roadmap: https://github.com/garritfra/cell/issues/22
Regarding your question: This idea has been sitting on my todo list [1] for over 3 years now. I don't usually work with large data files in my dayjob, but occasionally working with the odd CSV on macOS frustrated me enough to put it on the list. And now that spec-driven development has matured enough to be actually useful, there's no real excuse not to build this.
I genuinely see myself caring for this long-term. I'm comfortable with the scope, and there seems to be some real interest from the community.