The increase in technology cost is already geometrical, since it's also a prerequisite to research all previous ones. On top of that you have the increase over time modifier. If you add additional costs, it would be prohibitive for small countries to research technologies, even on time.
In the end there is a maximum tech level (33), and the ahead of time penalty makes sure that level ups are interspersed throughout the duration of the campaign. Because of you allow Ming to level up to level 33 by 1600, what is there left for them to research until the end of the campaign?
Personally I would love a simple tech tree rather than a linear progression, also dipping into the concept of institutions and institution spread... Here's hoping for EU5!