I was thinking about a more streamlined system for specific bonuses and penalties.
There would be three bonuses. Easy gives one extra d20, easier gives two extra d20, and easiest gives three extra d20. You roll your dice and take the highest>
There would be three penalties. Tough forces one extra d20s, tougher forces two extra d20, toughest forces three extra d20. You roll your extra dice and take the lowest.
If a roll is both tough and easy, they cancel each other out. If a roll would be tougher and easy it would just be tough, and so on.
So a Ranger with orcs as a Favored Enemy would roll two d20 when attacking an Orc. A Dwarf Ranger would roll three d20 when attacking an Orc.
It seems like it would be less math, but not sure it would more fun.
Have you not basically described advantage and disadvantage from 4th ed?
Maybe? I've never played forth.
I do like the idea. My concern is more about how you translate current effects across. And how the maths works out. I will try make a spreadsheet just now