Very nice. I've been agitiating for a system like this in GC3 for nearly a year.

I like the general idea a lot, but I woould like it even more if the requirements were somewhat randomized from game to game. Otherwise it just become another checklist every game to do to gain the tech you want.

I can't see how you'd find this too RNG dependant. Player Aaa might have those spiders close by, but player Bbb can expand more easily and get too unlock the 'Expansionist' research much sooner, or might have a Mine close by which player Aaa hasn't. If you want to make everything the same for each player, where is the fun in that?

Well, the tech I gave as an example was just that: an example. But yeah, sure, someone could start three wars in the beginning of a game just to unlock a tech... but... then they'd be fighting three wars...

The conditions and the tech benefits will of course have to be carefully balanced. I do like the idea of slightly randomized conditions, as Denryu suggested.

I agree, all leaders shouldn't have the same set of bonuses. Maybe it looked like I am strongly against this idea, but I am not. You have to understand that between an AWESOME idea, and a SUPER COOL feature, is a thingie called "implementation". Even though I am excited about this idea, I see a couple of issues, and it's important we discuss them.

I am a power gamer, at least I always considered myself as such (in other words: either I clear the game 100%, or I don't play it longer than 10h.), and I always think about an idea in terms of how something which can be exploited. The perfect case is when you implement a feature that is closely connected with reality (it reflects it well, therefore players will easily grasp the idea), and  (also) it's balanced. At first you admire features that are closely linked with real life (or just cool), but in the end you will always care about system mechanics and ways to 'break the game' - i.e., bend the game mechanic, so that you are closer to a victory.

If you don't understand what I mean, here are a couple more explanations and proposals.

• Unlockable techs HAVE to be equal in power (aka balanced), so that no player will skip them. Maybe it's easy to say, but when you have a tech tree available for every player, all of them can skip some poor techs, and develop the better ones. Here, we don't have such luxury - if an 'expansionist' tech is poor, then our sovereign has a problem (i.e. Bbb) .
• Conditions (which have to be met, in order to unlock a given tech) have to be well chosen. Each of these conditions have to have a well thought background and it should be strongly based on the game mechanics. In other words: if we implement a condition which states "Defeat 3 enemies" it means that we made a mistake. Defeating 3 bandits or 3 hordes of bloodthirsty demons is something different and such feats shouldn't be 'unified'. I also vote for no numbers in the conditions, as numbers are the easiest ones to get exploited.
  
• Due to those 2 statements above, I would propose that there would be no more than 3 unlockable techs for each tree. Every one of these techs should indicate that you really did something extraordinary which mattered in the game and wasn't an act to break the game.
• A couple of my proposals:
  • Victor [warfare]: You defeated an enemy sovereign.
  • Dragon Lord [warfare]: You 'tamed' a dragon.
  • Metropolis [civilization]: One of your cities reached maximum level of advancement (I don't have to say that such level shouldn't be easily obtainable).
  • Master of X [magic]: You learned all the spells from X domain. (X = Fire/Water/Earth/Wind)

Those are all good ideas. My example was just to illustrate the idea.

I think the advantage of such a system is that it would promote some unusual strategies. For example, instead of building a hundred cities you could just concentrate on developing one Metropolis so you can unlock the "Metropolis" tech and get whatever.

Of course, with the new "breakthrough" system there are essentially only 5 techs available. I'm fine with that. Maybe you could have unlockable breakthroughs?

Interesting idea.  Some of my favorite diplo wrangling in ToA is to get those unique racial techs.  So any kind of teching that goes above and beyond budgeting research makes for a little bit more interesting gaming.  But a thing to consider is that all the bonuses of these hard-to-get techs can easily be represented by any number of mechanisms.  E.g. why not just give the bonus to the unit that kills 10 other units, instead of making that the criteria for researching a unique tech?