As for the day triggers, they are not needed to begin with. The new engine makes events appear when they are supposed to rather then the day when they are supposed to. So they will not trigger if it makes no sense and will trigger when certain conditions have been met + MTTH (be it before or after the actual date). The decisions do the same thing: make an event happen when it is supposed to rather then at the date when it happened.
Even if the developers won't use them it's needed for the modders to create history better.
Even if the developers don't agree with the modders, at least don't remove the modders most important tools.
AFAIK I wouldn't even be able to continue my mod project over to HoI3 at all with the current mod capacity that exist (and if I can it seems like I would need to go kamikaze over the details everywhere).
And the below ones were stated to be wrong in this thread, so in a summary:
So we have: AI with historical goals,
No.
historical decisions
No.
possibly historical missions.
No.