Umhhh…I have a small difference in perspective here.
For general tasks like - run operations on this column, make graph, run regression on this data etc, I don’t think it will not be necessary for the codex to read the entire file.
That part will be handled by the Excel
All that codex will need to do is run the logic part i.e make the appropriate code.
I also saw a codex powered startup that promises to do so on MySql, Postgress etc
Please do correct me if I wrong 