Why do you think that linking brains together directly would be so much more effective than email?
It's a premise to a scifi story, where the topology is to be never discussed. If you are to actually think in the detail... how are you planning to connect your million brains?
Let's say you connect the brains as a 3d lattice, where each connects to 6 neighbours, 100x100x100. Far from closely cooperating team, you get a game of Chinese whispers from brains on one side to brains on the other.
Why do you think that linking brains together directly would be so much more effective than email?
The most obvious answer would be speed. If you can simulate 1,000,000 brains at, say, 1,000 times the speed they would normally operate, the bottleneck becomes communication between nodes.
You don't need to restrict yourself to a 3d topology. Supercomputers with hundreds of thousands of cores can and do use e.g. 6D topologies. It seems that a far more efficient way to organize the brains would be how organizations work in real life: hierarchical structure, where each node is at most O(log n) steps away from any other node.
If Strong AI turns out to not be possible, what are our best expectations today as to why?
I'm thinking of trying myself at writing a sci-fi story, do you think exploring this idea has positive utility? I'm not sure myself: it looks like the idea that intelligence explosion is a possibility could use more public exposure, as it is.
I wanted to include a popular meme image macro here, but decided against it. I can't help it: every time I think "what if", I think of this guy.