This thread has sparked a desire in me to mod the tech group maluses, decreasing them substantially for most groups.
Since every tech group has (& keeps) its own unit types, and idea groups are already set (preventing, for example, West African nations from colonizing South America outside the hands of the player or an intentionally randomized game), I'm not sure these tech penalties are even important.
These are the current penalties:
Western (+ High American): 0%
Eastern: 20%
Anatolian: 25%
Muslim: 40%
Indian: 50%
Chinese: 60%
Sub-Saharan: 60%
Nomad: 75%
Mesoamerican / Andean: 150%
North / South American: 250%
Those bottom two are also Primitives, which means no boats, reduced gold income, and trivial annexation.
I'm thinking something more like this:
Western (+ High American): 0%
Eastern: 5%
Anatolian: 10%
Muslim: 15%
Indian: 25%
Chinese: 25%
Sub-Saharan: 30%
Nomad: 50%
Mesoamerican / Andean: 100%
North / South American: 200%
Western Arms Trade drops to -5% (from -10%). Protectorate drops to -10% (from -20%). Notably, a Muslim nation with Western Arms Trade and minimum piety would now receive no tech penalty whatsoever.
With these changes, American states will still be trivially conquered by colonizers, but piercing deep into Africa would be substantially more challenging as the nations there would be much better able to offer resistance. I keep the 5% difference between Eastern and Anatolian so that the Ottomans don't get completely out of hand. I wanted to give Nomads even more of a break, especially for the Manchu, but I'm concerned about Muscovy. The PLC is technically buffed, but it Westernized trivially anyway so I'm not too worried about that. Morocco should be able to fend off the Iberians much better in the mid-game. The Ottomans do lose much of their tech advantage over the Mamlukes, which might create more divergent mid-games in that region. Persia will be much more important. Fewer nations in general will Westernize because fewer will be more than 7 techs behind, especially early.
I want to run a few observer games under this paradigm and see what happens.