So, in order to get a 2/0 opening in a 5-player game, you have to have 5 players, with you being last, Noble Brigand and Cutpurse on the board, your first opponent open Noble Brigand, the next three open Cutpurse, you start with a $2 hand, have all the cutpurses get drawn t2 and played, with you having drawn 2 estates as the next two cards. If we spot you the kingdom and that all of your opponents are playing this way, the chances of everyone drawing these hands is... 1 in 217,728. Pre-post edit: I suppose player 2 can buy noble brigand instead of cutpurse and this makes things much more likely; however I also didn't take into account the possibility that NB flips double estate for some of the opponents. Well, I'm too lazy to fix it now.
Regardless, you certainly want to buy something here anyway. Probably copper, though maybe a t1 estate. Anyway, this leads to the case where you want to open duchy/estate: You're last in a, I don't know, 20 player game. They're opening noble brigand and cutpurse everywhere. Piles are obviously going to run in about 3 seconds. You'll probably never really have much money - silver will get NBed away 20 times, and copper will get cutpursed down. There's no decent cheap virtual coin or draw, and cultist is on board, so you can run out the ruins fairly comfortably. The points here almost ensure you victory, as everyone else races to get $2 enough to get second. Also, they increase your chance of getting gifted copper by NB. Heck, this could maybe even turn into an argument for estate/estate, if you get 2/5 and cutpursed down off the 5 to a 2 or something.
I am otherwise not convinced for these openings, and especially not for curse/curse.
Oh, and for 2/2 opening from 5/2, apart from estate/estate as mentioned above, what about chapel/squire with like familiar or goons on board?
However, I think I may have thought of some others (edge case me braaaahhhh):
-Never open Duke
-Never willingly trash every card in your deck.
-Never spend $5 on a turn one feast
-Never open Village/Village (the specific card, not the type)