Funny thing I'd like to mention.
We have a customer with multiple sites where one site has a server that hosts RDP sessions for employees scattered thoughout the other sites.
On the MX'es on the branches the MX perfectly recognizes Remote desktop traffic and uses the correct uplink selection and DSCP tagging.
However at the site where the RDP host is at it does not recognize the traffic flowing back to the other sites.
So I ended up adding a rule matching on source port 3389 for the uplink policy and even localnet:ip for the DSCP tagging.