The propper back end sounds like it would not be sufficent to use normal hosted servers. Data centers normally use standard ethernet between machines, running at 100 or 1000 mbit, depending on how new they are. Darkstar nodes will be after something faster than that, like infiniband, which starts at 2gbit and goes up to 96gbit (according to wikipedia). I think that would be harder to find in a hosted environment, and certainly won't be cheap.
On the bright side, see this
post by Jeff to see how us small devs will be able to get hold of back ends.