Out of curiosity, what would you say is hardest constraint on this (brain replication) happening? Do you think that it would be an limitation on imaging/scanning technology?
This ignores neurons since there are only like 86 billion of them, but they could be sufficiently more complex than synapses that they'd actually be the dominant factor. Who knows.
This also ignores glia, since most people don't know anything about glia and most people assume that they don't do much with computation. Of course, when we have all the neurons represented perfectly, I'm sure we'll discover the glia need to be in there, too. There are about as many glia as neurons (3x more in the cortex, the part that makes you you, coloquially), and I've never seen any estimate of how many connections they have [1].
Bottom line: we almost certainly need exaflops to simulate a replicated brain, maybe zettaflops to be safe. Even with current exponential growth rates [2] (and assuming brain simulation can be simply parallelized (it can't)), that's like 45 years away. That sounds sorta soon, but I'm way more likely to be underestimating the scale of the problem than overestimating it, and that's how long until we can even begin trying. How long until we can meaningfully use those zettaflops is much, much longer.
[1] I finished my PhD two months ago and my knowledge of glia is already outdated. We were taught glia outnumbered neurons 10-to-1: apparently this is no longer thought to be the case. https://en.wikipedia.org/wiki/Glia#Total_number
[2] https://en.wikipedia.org/wiki/FLOPS#/media/File:Supercompute...