They appear to have changed it. The only PvP related mission I've gotten since the patch was for a token (clickable) that will reward 1000 honor and 1000 conquest points when clicked. Obviously I banked it for now, since clicking it would probably not actually give the conquest. I'll click it after the season starts.
But I haven't seen any of the old gold/honor missions since Tuesday.
Yeah, it seems like the trigger for these missions is doing some PvP.
I was getting them on my warrior for the entirety of WS1. Only did some random BGs, farmed about 5k honor for transmog I wanted. Since that day I've been constantly receiving honor + exp and honor + gold missions, farmed over 20k honor with these missions throughout the season. I didn't needed to do any more PvP that season, when it actually ended the PvP missions stopped.
So the trigger seems to be a certain amount of PvP in a given season.
I did some testing and my conclusion is the trigger is 4000 honor gained in the current season. Doesn't matter if it is BG or Ashran. Zero Coliseum Sanctums.
Char 1
5433 honor (~70% gained in Ashran)
Got 1 honor mission in the following day(And got +3 total missions up to day, one of them was 200honor+gold).
Char 3
4510 honor (100% Ashran, 2 wins 8 events)
No mission yet. My guess is that I don't got the mission today because I went over 4000honor at 23:00+. Tonight I might have it.
Char 4
4152 honor (100% Random BG (16 total, 35% wins :s))
Got 1 honor mission in the following day.