Creating two worksheets and two dashboards is definitely one option. You might look at the options in Displaying Different Number Unit Abbreviations Based on Number Size as well. Ultimately the ability to change the number formatting automatically based on how big the number is not built into the product
The Tableau website has an Ideas section where customers can add, comment, and vote on features they would like to see in the product. Votes are used to help prioritize new features. Our Development team also loves to see everyone's use cases in the comments, which helps them better design features that will meet the most possible needs.
To voice your support for the inclusion of this feature in a future product release, add your vote to the following Community Idea: Smarter Number Abbreviations
Hope this helps