I just submitted the first PR for changes around this: https://github.com/triplea-game/triplea/pull/1750
It primarily focuses on the following updates:
- Remove 4 old AI Bonus properties
- Add new Bonus Income Percentage for each nation (not same bonus for all AIs)
- Add bonus income during end turn phase instead of purchase phase (so you aren't multiplying saved income from the previous round)
This is just phase 1 of changes I'm planning to make for AI bonus properties. I'm also planning to have future PRs address other resources (non-PU) and look to add per map properties that can be configured.
Once its merged, play testing and feedback strongly encouraged!