I was thinking of a new way to do a tech tree when that comes up. With most stratagy games we see, the tech tree is static and the same across all factions. wait x turns until this new thing becomes available to us then we can begin production of this standalone unit/structure. What i was thinking was a more fluid design where the whole point is to improve existing technology; put enough effort into some topic and you get a "eureka" where some scientist creates some revolutionary improvement. For instance select improve spears to improve their damage through new modifications like serated tips or poison dipped tips. Eventually you'll max out on what the tool can output and so as you're progressing with your improvements you'll get an ever increasing percentage chance of achieving that new eureka item as research progresses (with a 100% once the item's abilities are maxed out). Also i don't think it would be very immersive to show a direct tree branch link between tech x, which progresses to tech y, finally to what you need with tech z. I think it would be cooler if when you get a eureka the game rolls for a new technology to unlock in that category (it would be stupid to unlock a new food producing technique by putting your research efforts into armor). This would provide tenser moments where a player has to cross their fingers to hope for the specific tech they want to beat a situation (i.e. better weapons to stave off rapidly encroaching Masklings). A point i forgot to add would be that in games like civilization, i hate how there is no cultural difference between empires in tech (besides 2 specialized units); throughout history we see different nations investing in different concepts that work with the land their given to end up with drastically different item designs from those across the world (EX: 17th century Europe with advanced ships that could decimate any navel force in the Indian Ocean with breeze, or even the Russians pushing both Germans and French out due to them not paying enough attention to winter clothing nor food supply lines). Things like this would make every game very unique and not so predictable that experienced players will always know what route to take to maximize their situation.
Sorry for the long post I hope this sparks some creative ideas among you guys.