Since I read that Ideology tree is going to be one of the first things finalized, we probably should talk about it here fairly quickly.
So far: this is what I don't like about it, and what I'd implement if possible (most likely expansion pack required)
Caveat: some of this stuff may shine more once the games last longer and as the beta progresses, I am basing off of very rough alpha feedback here.
1) It has that "filling buckets" feel. It doesn't feel like the ideologies are in conflict. I don't know if this is really changable though- maybe in an expansion. It's not a gamebreaker, even if it feels a lot like Social Policies from Civ 5.
2) My suggestion right here: Events need to pop up that have extra options triggered based on ideology, either by ratio of ideology points, or net ideology points, or both. The best example of this being done well would be some of the events in FFHII (and well, you've got Derek right there for advice on how to pull this off) I think this is what's needed to make the system "effectively fun", though I could see some folks not liking it as "random". (This is what I'd implement for the base game- if possible I'd hide the extra choices unless you had the trigger to keep an element of discovery in the game)
This would probably take a good bit of design work though, as you'd have to script a large number of events so it doesn't become random/predictable.
If you ever add Mega Events back into GC3, you'd probably want some of these events to have a chance of triggering a Mega Event through unexpected consequences (maybe 1% chance on some choices)