Currently the UserSearch in DNN does not index Username or Email address. We should capture that so they can be searched upon. They should both by default be restricted to Admins or the Users him/her self only.
We should also try to enhance the current logic where everything is being dumped in SearchDocument.Body, instead we should use custom keywords so at the time of querying structured data can be retrieved.
There are few dates that can also be added in the SearchDocument (e.g. Date User was created). This information can be used when someone uses the SearchAPIs to perform custom queries and sorting.