Here's the general plan with poisons.
All of them with have varying levels of potency. Poisons found in the wild will always be of the lowest potency levels, with crafting required to get the highest. Taking a poison found in the wild and crafting it to mid-tier potencies will not be overly difficult, but crafting the highest potencies will be both difficult and likely require additional ingredients.
Poisons will have onset timers that will be largely based on potency. Lower potency poisons will generally take longer to kick in, higher will affect you more quickly. But there will be a good bit of variation among poisons. Some of them will be intended to be quick onset, while others long. I expect this will make poisoning someone's food/drink a more viable option than today, as it may take a while to kick in and they won't necessarily know when they were poisoned.
Many of the poisons will have various effects based on potency as well. For example, low potency peraine may take a few minutes to kick in and only make you feel sluggish and slow, lowering your agility or giving you the slow affect. It would require higher potencies to actually paralyze someone, and even then not likely right away.
Poisoning weapons will still be possible, but the poison will fade over time losing potency before finally being useless. Each of the poisons will be more adaptable to certain methods of poisoning, so for example poisonX might be more suited for coating weapons and so won't lose much potency, whereas poisonY really works better in foods, so if you try to coat that on a weapon it dramatically loses potency.
Cures will not be an instant cure, but will be more like an antidote that works over time. Cures will also have potency and so the more potent a cure is, the more effective it will be against a poison. Lower potency cures may not even actually remove the poison, but will instead just lessen the effects. There will also be some other methods introduced to lessen the symptoms of poisoning. For example, "drink the special tea and it will take away the nausea", reducing the harmful effects of terradin. Taking a cure proactively will give some benefit in resisting poisons.
There will be no such thing as a total saving throw to completely resist a poison, but successfully saving against one will dramatically reduce its effects.
A handful of new poisons will be added to the list of existing poisons - none of which are going away, though many will be altered to take potency into account. Availability of ingredients will be added to SimDesert, which means their location will have a large random component. Instead of knowing that "terradin is found on the bush in this exact spot", it will be more generalized areas: "Terradin will be found somewhere in this half of the forest". The poisoning skill will aid in finding these in some capacity.
There are other features around this that are still being worked out and discussed, if they happen at all. Among these are:
a way to better identify your cures
foraging for some poisons/ingredients
building immunity
With all that said, this is going to be a very long-running project. My general plan is to work on one poison at a time until it's where we want it, then move on to the next, with appropriate announcements as they're done.