After some more digging I found this in the /usr/lib/systemd/system/Xvnc@.service file.

[Unit]
Description=Xvnc Server

[Service]
ExecStart=/usr/lib/vnc/with-vnc-key.sh /usr/bin/Xvnc -noreset -inetd -once -query localhost -geometry 1024x768 -securitytypes X509None,None -X509Key /etc/vnc/tls.key -X509Cert /etc/vnc/tls.cert -log *:syslog:30 -extension MIT-SHM
User=vnc
StandardInput=socket
StandardOutput=socket
StandardError=syslog

So it seems that it is now a systemd service and instead of having a single service support multiple sessions. You now have to have multiple services to support each session.
How is this better than it was before ?