Letting minors catch up in tech is something I've been wanting for a while! It could be as simple as increasing the rate of tech diffusion every time the world becomes more and more connected, or globalised.
Ideologies and conflict between them would also be a neat concept to introduce for the late game.
Having to adopt free enterprise to catch up in tech would feel weird seeing as global corporations actively exploit the "tech" disparity between producing nations and consuming nations. I think rapid modernisation in nations has historically been achieved through heavy control of the economy by the state or state-supported corporations.
To add to this, I do feel like natural religion spread could use a makeover to be less random (though I do not know at all how it currently functions)! For example, trade routes from cities with (core or historical) religions could ensure an eventual spread to the receiving city, if it lacks the respective religion(s).I think Indonesia should start with a Hindu Guru in order to ensure the possibility of building Prambanan (and because 'Hinduism' was already widely present in Indonesia by 650). A second starting Buddhist Bhikku would also be reasonable to help kick off the spread of Buddhism in your island hopping, relying on natural spread is woeful!
4) More wars between France and HRE (Italian Wars, see point 1).
When I play as France I never invade HRE because of prussia spawn