I am not sure what you mean by
But isn't it impossible to predict anything like this with an entirely new way of building GPU's on its way?
But the way I see it both manufactures are talking about heat levels exceding the total power consumption of most "laptops" these days, and I see no reason for them to lie. Therefore, I see the only option, at least in the vast majority of cases, being either down clocking or smaller and cores. Down clocking is probably the better option because the voltage can be dropped as well. I think that unified shader architecture, that ATI is going to be using is a good bet due to its extra flexibility.