There aren't a lot of things you can do with a Project (without radical additions to the XML, which I want to stay away from). We can do:
- Intercept Nukes
- Change maintenance modifiers (global, # cities, distance, or connected)
- Free techs if known by certain # of civs
- Special unit or building that can be built by anyone only after the project is complete
- Worldwide trade routes (all cities, regardless of owner)
- Global health/happiness (all your cities) or world health/happiness (all cities)
- Global commerce (+X% gold/science/culture/espionage all your cities)
I did consider a split health bonus: +2 health to all cities worldwide and +1 health to the owner's cities. I also considered a small commerce bonus, but I think that is used too much. I really can't think of any other very appropriate effect to tie to Penicillin. Would splitting the health be a good idea?
As far as the proliferation of health goes, I noticed on my current game (Large/Noble/Standard speed) that around the Industrial Era, cities were close to their health cap except for the additions of Hospital and Water Treatment Plant. One thing that I was thinking of was to increase the unhealthiness of the Renaissance and Industrial Era dirty buildings (like Foundry, Factory, and others) by 1. By the Transhuman Era, you shouldn't be worrying about unhealth, but it should be a factor before that.