We currently using a custom realm based on a custom JAAS security domain based on a custom JAAS login module in WildFly 10.1. The custom login module is based on the PicketBox DatabaseServerLoginModule. We use a subclass because we have to perform additional checks and block the user after too many logins.
Looking at the upcoming changes in WildFly 11 with Elytron we would like to know:
It should continue to work. However, you can already try Downloads · WildFly
And yes extending JdbcSecurityRealm in your CustomRealm seems to me doable. You can also try to do that.