I face the issue, that I would like to work with multiple typo3 instances that access only one fe_users table from one "primary" instance. The idea is to "plug" typo3 instances on a primary instance but that the plugged typo3 instances are not having an own fe_users management.
The instances are not necessarily running the same version.
It would be best to use a single sign on solution for this or a central directory. Since every TYPO3 instance could have a different structure of the fe_users table, there will be problems using a single database table. Another option would be to synchronize the records with a cronjob between the instances.