I can confirm that poison resistance over 100 does heal you from poison instead of hurting you. It wasn't much, since I only had like 105% PR.
Thats good to hear. It means that the mechanic is already there.
All that needs to be done is to enable resistances to specific element to slow down the speed at which you gain damage and slightly minimize the damage from that element.
I cant give proper or exact numbers for that myself, but i trust the devs can do that to fit with what they want for the game - relatively easily.
Speaking in simple terms, someone with 30 % fire resistance (or poison) would be damaged a bit less and a bit slower, then one with 0%. One with 50% would be damaged a bit less and slower then that - and so on - until 100% when you would start to heal from the fire.
Or poison.
