Khaelis
Plantera
extremely situational and almost never worth the investment, I say. The only 2 that would be worth anything is poison for Queen Bee/Plantera and cursed flame for Twins. Maaaaybe a fire resistant potion would be handy while in the underworld, but all others would never see any use because it's hard to know WHEN you're going to get hit with any debuff just out in the wild, and even if you do get hit, they generally don't mean anything major. It's only the DoTs during boss fights that make a big impact, and it's not so much that you are taking damage as it is your life regen has halted. Electrified (martian invasion) debuff is another of the very few problematic ones.
All in all, the debuff immunity potions would be pretty useless except is specific circumstances where they would be the best thing ever. It's one extreme or the other. Take that as you will.
This is what I was thinking as well. But when it comes to Potions, there's not a whole lot you can do without going overboard.