In the USA, it appears that the threshold for promotion from D.IV to D.III for teams that don't win their playoffs will be first place in their conference and 18 or more wins - with some 18-4 teams missing out based on PtsD. It could go to 19-3 if there are many teams with better records knocked off in the finals.
As it turned out, one team with a 17-5 record was promoted.
There were 34 teams that were both conference champions and playoff winners that promoted automatically. There were 36 conference winners who did not win the playoffs, but were promoted as part of the bot cleanup. And there were 13 teams that won their conference, but failed to promote either as the playoff winner or the bot cleanup.
In the 39 D.IV leagues that were relatively full, one of the conference winners won the playoffs in 29 leagues (74%).