First off, wow! Thank you for the responses so far - I'm definitely feeling encouraged to go ahead and wrap up the demo so I can put a link up for you guys to play with!
At the moment, I'm actually tuning my "test units" to make sure that it really shows off the idea without requiring you to mod it first. In the first version, I'll probably have all the "create your own units/abilities/effects" options turned off, so the focus will stay on how easily all the nuts and bolts fit toger... plus I've got this crazy CNF things I might put in for the tag requirements... lol.
Is it using the same core mechanics of elemental? Yes, mostly. The concept of an ability is pretty much the same, only now there's a distinction between "Action" and "Reaction" abilities. Additionally, I've added "tags," which are like "keywords" from Magic or "types" from D&D. When you get right down to it, other than the combat flow, everything else is just extending their current model.
How radical a change would potentially have to occur in programming? This one is a tough question, but I'll answer it like this: I wrote all the game mechanic interactiosn from scratch, by myself, and in my spare time over three days. I'd imagine a team of programmers who already had a model that some parts of this mostly extend could do it in a week or two.
Is it AI'able? How quick is a round? What's it's "go" style? It's I go, you go. At the top level, there's one "Active" player who moves all his units, then the next player becomes "Active." But, each time you "declare" an action for one of your units, your opponent declares one reaction that is "provoked" by that action, so the game proceeds along a very quick "I decide, you decide" path, where the turns are much more interactive, and turns are quick.
Is it expandable, i.e. down the road a year can abilities still be added? IMHO, this is the absolute best thing about it. It's so freakishly customizeable that it's surprising. In my current (working) model, almost everything is moddable - unit stats, abilities, effects, required tags on target units, provoking units and provoking abilities. I'm currently cleaning up the part that applies tags to stats granted from equipment. For convenience, the "core attack resolution" is hard coded, but I have some great notes based on expression trees for how to get that moddable quickly
Get enough people playing it, profit! (even if only in terms of getting it in the game) The biggest thing for me would be seeing it in a real game!
I'll try and finalize things for my first demo post this weekend (I've got a birthday party and a wedding to attend first!),