Commented by: @dyemanov

I tend to object to this request. First of all, it allows a non-privileged connection to obtain a possibly sensitive information (user account, client IP address, etc) about another connections, and it looks like a security weak point. This is exactly the reason why non-DBO/DBA users don't see other connections in the MON$ tables. Second, extending the error message with possibly varying information (tomorrow you might need PID of the blocking process or its Windows logon name) doesn't look like a good idea at all.

That said, I believe that a better approach would be to grant a regular user abilities to see other connections in MON$ tables. This way you may explicitly decrease the security level to the threshold you need. And this is already planned for v3.0, see CORE2557.