A longer classical era would be pretty nice, but that could almost be done by reassigning medieval techs as being classical. And adding just a couple more.
I also think that the industrial and modern ages are actually about the right left and cost. The only real problem is with the way great scientists work and the possibility of bulbing the entire modern era.
The real place new techs need to be placed, IMO, is in the renaissance. For a start it should be split in two. The renaissance followed by Enlightenment. They were drastically different. The renaissance is the discovery of America, the rebirth of greaco-roman thought and the wars of religion. The enlightenment is the napoleonic wars, independence of America, colonisation of Africa/India. The two are two completely different historical periods with completely different styles of thoughts.
Adding it in would also make a lot of sense from gameplay. It would put more distance between the cannon and arty, and between muskets, rifles and infantry (which are all pretty rushed).