Leavers in Duty Roulettes

[Canadane]

Technically that's already there. I think if you leave from a duty 3 times, you forfeit your right to go into DF for the rest of the day. I think that also applies to withdrawing from the commencement screen.

If you withdraw from a ready duty 3 times you'll get the 30 min penalty. You'll continue to get another 30 minute penalty for each further withdrawal for the day.
If you are the first to leave a full party in a duty, you'll get the 30 min penalty.
There's no escalation beyond a 30 minute lockout. Nobody gets locked out for an entire day, that'd be a bit harsh even for SE.