This was an idea I had floating around in my head for months (don't ask ... my head is a weird place), but I never had the right idea of how to achieve that. Until yesterday. Somewhere between breakfast and lunch, I suddenly got the idea how it could work and after running into some trouble, and subsequently running around in circles, cursing, someone gave me the idea of how to really make it work.
And now it seems it works.
This mod changes the harvest chance based on you Alchemy skill and your Luck.
Per default you get:
0.4% per point of Luck, like Luck works for other skills.
Alchemy 0-24 (Novice) - -15% chance
Alchemy 25-49 (Apprentice) - no modifier
Alchemy 50-74 (Journeyman) - +15% chance
Alchemy 75-99 (Expert) - +30% chance
Alchemy 100+ (Master) - +50% chance
Additionally, a master of Alchemy has a 10% chance to harvest a second ingredient.
This would mean that a Journeyman of Alchemy who has about 12 Luck will have a 100% chance of harvesting those common ingredients. A Master of Alchemy with Luck close too 100 will get a 70% harvest bonus which will allow them to harvest all vanilla plants 100% successfully (except for a few SI ones). I personally don't think that's too overpowered, but everything can be customized in the mod's ini file.
A more fluid progression that allows constant calculation of your bonus instead of waiting for the next mastery level can be turned on in the ini file, too.
Nirnroots remain unchanged.