We have a new feature that is designed to accomodate this. This is called the Online Sync client feature, check out this intro to it for more information: Keep Your Data Fresh with Tableau Online's New Sync Client Feature | Tableau Software
Unfortunately there is one big caveat: this won't work with WDCs that require OAuth authentication. So the only way to make this work for the Google Sheets case is your Google Sheets public (at least accessibile to anyone with a link).
If that isn't an option for you, please feel free to make a new post on the Ideas forum for this feature request, that's always a really helpful way for us to see where the biggest pain points are for our customers.
Associate Product Manager