From the interviews I've heard with the founder, rPi set a price point first, then developed the best hackable computer they could to match it. If they keep up with that (as they have so far) then expect something more powerful and possibly smaller at the same price. Although I think the rPi zero is probably at the lower end of how small you can go without making tinkering cumbersome with all those gpio pins and such. although, people also like ATTiny, so who knows :)