The Input Tool reads Excel however many dashboards require multiple people to update a spreadsheet. Excel is too much of a hassle to share and update. Being able to read directly from a Google Spreadsheet would allow easy multiuser access to updating spreadsheets for dashboards.
Please add Google Spreadsheets to be an option in the Input Tool.
Can you also consider adding "calendar" inputs ? Calendar events are used as an input for many applications today in business and doing it manually takes time. a native input function will fasten it a lot.