Null Vote here. I do like the idea, but this is just how I can see the results.
I suggested in the past to increase the drop rates for potions because they don't really get used. However, with the game changes since then, it has become a little bit more balanced for Softcore and only Softcore because of "Death Farming" and the speed in which the "Seasons" are Reset.
Your #1 Rework idea: "Lasting till Reset": I like this idea, I play Hardcore and store up potions for the next season and have a monster character build that will last for a year. Now if I was a Softcore player, I would hope the season at least lasted 6 months.
Your #2 Rework idea: "No Stacking Effect": Again, I play Hardcore and this would make potions even more useless because I can not make a monster character build if "Your #1 Rework idea" was implemented. Now for Softcore, it would hinder anyone wanting to purchase and stack up stats for their "Death Farming" character.
Your #3 Rework idea: "Adding Event Modifiers": Not a bad idea, would think this would be a nightmare to code in, and may cause a ton of errors to the game? Imagine a full group of players using a ton of different or same modifier potions. Does the entire group benefit (Stack), or just the killing blow? If is "just killing blow", then what happens to the "No Trapdoor" modifier? Can you see the issues this could have?
Hey, none of the above is meant to be a negative, it is just an indicator to how it could (not would) affect the mechanics or game play. To me it is not balanced.