Support for Excel for custom widgets
Dash currently supports CSV files for custom widgets. It would be nice to be able to directly read from an Excel file, though.
Many people have complicated spreadsheets with their source data, and then have another workbook in Dash's format with calculated cells. Every time they edit the spreadsheet they have to then export the workbook as CSV so Dash can read it.
If Dash sees a file that ends in .xlsx it can just show a dropdown form them to choose which workbook they want to use.