Well i only saw a video from some random guy on youtube about SCII, but the only interesting thing i saw in there was arbiters being like "mobile pylons", and the fact you can change the angle of the screen.
I personally think i wouldn't play SCII for a while after it's released, because i didn't get SCI... fairly, but if i wanted to get SCII the same way it would take about 4 days for me (some friends tried it, so i'm not making up stuff >.>).
Now on to the concept, here's some ideas that might fit in:
It would be nice that each faction has a spot where they get some units representing the number of kills they have. These could also be mobile units, so that each faction chooses where to send those units to (not themselves, of course). This would also enable you to implement spells like "kill steal", where you could steal a number of kills from another faction, or "kill absorb", where all your kills are given to yourself as new units. The drawback to this is that you'd have to implement a system to force players to share their kills rather than just massing them in their storage or waiting for "kill absorb" to be available. Although maybe i'm going too in-depth in these systems for a concept that's not even being worked on yet.
Another nice idea would be if, for every X kills of X unit you got a hero from a unit of your race equivalent to the unit you've killed X times. For example, if you're Hell (i'm assuming Heaven: Protoss, Earth: Terran and Hell: Zerg), for every 50 zealots or marines you kill, you would get a hero zergling.
A last idea is that for every X kills (i'm assuming there are multiple factions within each race) Heaven or Hell makes, they would increase their chance of getting a unit from every kill Earth makes against Earth. In Earth's case, they would get and then increase a really slight chance of getting units from kills that Hell makes against Hell and that Heaven makes against Heaven.
EDIT: I also forgot to say this, but i agree with David, how would you even win? You haven't clarified this yet and i think if people knew, it would be a lot easier to give out ideas.
None.