This is in our backlog, but votes and comments about how you would expect this to work are very helpful to our planning/designing the feature so please keep them coming.
Also, for some scenarios in this space Access Reviews (https://docs.microsoft.com/en-us/azure/active-directory/governance/manage-guest-access-with-access-reviews) can be a good way of removing users who no longer need access, including those who don’t have accounts anymore. (Thanks Shawn for pointing that out for everyone!)
/ElisabethJames Mayhair commented
Any direction from the product group would be greatly appreciated.