Ability to connect multiple admins to one RDP session
The ability for multiple administrators to connect to one RDP session would really help in situations where you diagnose a problem and want
a colleague to look with you.
Agowa awoga commented
This feature is already implemented and is called "Shadowing". Just enable it and then you can connect to another session by "mstsc /v:SERVERNAME /shadow:ID /control" where ID is the session, you can query it by "quser /SERVER:REMOTESERVERNAME"
You can change this is the OS its not an app thing. Group policy or remote connection settings in network connections. Google it for windows 10