Maybe the solution is to come out with a few different techtrees to choose from. One that has the standard eras, a couple more that have added eras. Players can decide for themselves which one to used based on their own preferences.
BTW someone argued that the Renaissance is part of the Medieval era. This is not true IMO. The reason there is a seperate era called the Renaissance is because, we see a distinct revival of classical antiquity, and a loosening of the rigid religious life of the Middle Ages. Learning became more profound, simply because knowledge began to pass from hand to hand more freely after the invention of the printing press. It was not just monks in their monasteries who were educated, or high born nobles anymore. More and more people were able to acquire books and writings. The ability to learn, along with the dedication to history, art, science, philosophy etc. Brought the world onto a new stage of innovation. The end of the Reconquista in Iberian Peninsula, led to another new wave of learning as latin manuscripts were deciphered and translated into other languages. The Reconquista also led to the discovery of the New World
With the Renaisscance came the Black Death, weakening the church, which had no way to fight the scourge devouring so many people who depended on belief in their faith. We see a huge battle between church and free thought. Namely the Spanish Inquisition, which resided over trials of heresy, and witchcraft, culminating in the burnings and deaths of countless people. The corruption of the church also became a huge problem. The selling of indulgences, simony, and the printing and spreading of the Bible, led to scriptures being reinterpreted by the laity. This caused new viewpoints about religion, which inevitably led to Martin Luther writing the 95 Theses and pinning them to the door of the church at Wittenburg. This lead to the Protestant Reformation. Etc, Etc, Etc.
The Renaissance was a progressive age, during which the old ways of the Medieval times fought like hell to keep things from changing. However, nothing stops progress. Progress is like nature, it always finds a way.