On booting a new installed xenial with trinity tdm I get the error message:
"A start job is running for Hold until boot process finishes up(time/no limit)" which prevents starting the console logins.
Using sddm or lightdm works together with systemd.
I have looked into the systemd configuration of them both and changed the file
/lib/systemd/system/tdm.service according to the sddm configuration to

[Unit]
Description=Trinity Display Manager
Documentation=man:tdm-trinity(1)
Conflicts=getty@...
After=getty@...

# Ordering
Conflicts=plymouth-quit-wait.service
After=systemd-user-sessions.service plymouth-start.service plymouth-quit-wait.se
OnFailure=plymouth-quit.service

[Service]
# temporary safety check until all DMs are converted to correct
# display-manager.service symlink handling
ExecStartPre=/bin/sh -c '[ "$(basename $(cat /etc/X11/default-display-manager 2>
ExecStart=/opt/trinity/bin/tdm
Restart=always
RestartSec=1s

With this file the plymouth/systemd handshake seams to work.

Maybe this helps someone else.

Stef