"The ''Poison Absorb %'' and ''+ Poison Absorb (points)'' properties, we know they exist because some monsters have them, the same way they already exist for fire, cold, lightning and magic."
Kinda meh idea, because it is damage over time and that's a problem. With poison absorb added, devs must increase poison damage of most abilities, 90 max res and PLR makes you barely take any damage anyway. Another element damages are single and instant and for higher tiers they are required because even 1,2,3% from high amount is big for survability.
For 3.0 i have not much ideas, just one simple and maybe write later about anothers
I would suggest adding 4th archer in Tran Athulua with poison element. This way the charm from 1st lvl challenge contains every element, even -5% enemy poison res will help in early based poison builds that do not contain any "passive pierce" from skill tree.
I am not that much into d1 lore so not sure if it fits somehow.
Also using monsters from diablo1 that you meet from act1-4. You only meet them once or twice. They were present in fun season. Maybe single dungeon/rift with them?