As of version 0.9.13:
In nodejs, the XLSB and XLS formats easily support the specified dimensions. Just tested with an XLSB file with the specified dimensions and the
xlsx command took 11 seconds to produce a CSV.
The XLSX runs into a hard 256MB file limit (see https://github.com/nodejs/node/issues/3175 for a discussion), which based on my tests comes to about 5M cells total.
Web browsers have a lower limit. We haven't done precise tests but 1M cells works in Chrome.
We will need to rework large parts of the XLSX parsing to avoid hitting the limit.