It seems a lot more elegant/efficient/sane to me than trying to squeeze more and more racks into one building. So that's why I'm asking, as I think the benefits are clear, much better scalability, fairness (or getting as close to it as the exchange wants), cheaper (no need for fancy hardware), probably it would attract more market participants (lower barriers to entry).
It's the same hypothetical "EC2 model" without the meta-game of trying to get closer to the cores the exchange runs at a given time.
Can you elaborate on the downsides besides security?