Don't worry about pp gains. woc's system will work quite smoothly. Full rainbowing a song is very difficult. The mods will make it easier to get max points or at the very least closer to max points than if you just went through the map and did the same performance without said mod. It's kind of counter intuitive to say it is making it easier by making it harder, but it's really a difficulty tradeoff. You must deal withmod impairments in return for better point returns.
And really that has nothing to do with applying score multipliers for keys. With the way woc is treating multipliers, adding equal multipliers to higher key mods seems less of an option. It doesn't make sense that a non-7K map changed to a 7K map would be worth more points overall than a 7K map. If the ceiling remains 1,000,000, then I don't think weighting the mod at a gain is even feasible.
And really that has nothing to do with applying score multipliers for keys. With the way woc is treating multipliers, adding equal multipliers to higher key mods seems less of an option. It doesn't make sense that a non-7K map changed to a 7K map would be worth more points overall than a 7K map. If the ceiling remains 1,000,000, then I don't think weighting the mod at a gain is even feasible.