Needs some discussion first but this is along the lines of the following: -

1 - Within WildFly where we currently have realms we have an ability to query them to check they are ready to handle requests - this is mainly used for out of the box where we can display an error page describing to the user additional steps they need to perform.

2 - Realms are essentially the interface to back end stores of user information, most likely being remote with no guarantee that they are always available, from an Elytron perspective this adds an additional two options: -
i. Alter offered realms also taking into account availability, information disclosure risk but worth considering.
ii. Security status panels within admin console, view at a glance what is available and what is not allowing administrator to take action. We also have notification support - a candidate for a notification.