What's unclear for this kind of scheme is what impact it has on stacks or dynos that can actually take concurrent requests. There's the distinct possibility tha

What's unclear for this kind of scheme is what impact it has on stacks or dynos that can actually take concurrent requests. There's the distinct possibility that a concurrent server will see its average time get worse under such circumstances. People simulate their stack quite quickly, but do not necessarily simulate what might happen to other ones. Otherwise, it also means that you'll possibly have twice the data flying around your network due to the overhead of routing from one layer to the other one. Effects of these may be hard to predict. It's also difficult to know what the impact would be of a router that handles a lot of traffic for an app being cycled or replaced, or crashing. Does this mean you create single point of failure for apps? Do you go for redundancy, failovers, sharding or anything else to fix this? What about netsplits between units across layers? Random distribution has the advantage of generally being pretty reliable across all of these scenarios.