Well, for example, physical simulations using finite element or boundary value approaches. Pretty much anything you'd use with MPI or do on a supercomputer is going to run better on a machine with a nice network stack like this.
Even large scale storage (think backtesting on petabytes of options data) that uses a map-reduce paradigm and is properly sharded for the data access paths and aggregates would benefit from something like this.
There is a 2015 paper [1] that argues that improving network performance isn't gonna help MapReduce/data analytics type of jobs much:
" .. none of the workloads we studied could improve by a median of more than 2% as a result of optimizing network performance. We did not use especially high bandwidth machines in getting this result: the m2.4xlarge instances we used have a 1Gbps network link."
Granted things might have changed by now, but I am curious to see how and by how much?
[1]: https://www.usenix.org/system/files/conference/nsdi15/nsdi15...
Some map reduce loads, especially the kind that people running spark clusters want to do, end up moving a lot of data around. Either because the end user isn't thinking about what they're doing (95% of the time they're some DS dweeb who doesn't know how computers work), or because they need to solve a problem they didn't think of when they laid their data down.
I guess I cite myself, having done this sort of thing any number of times, and helped write a shardable columnar database engine which deals with such problems. If you don't want to cite me; go ask Art Whitney, Stevan Apter or Dennis Shasha, whose ideas I shamelessly steal. FWIIW around that timeframe I beat a 84 thread spark cluster grinding on parquet files with 1 thread in J (by a factor of approximately 10,000 -the spark job ran for days and never completed), basically because I understand that, no matter how many papers get written, data science problems are still IO bound.
Physical distance between the machines in a DC prevents RAM style "shared-memory" architectures, at least ones that aim to have 30~60ns access times (10-20 meters). Unless there are new paradigms for computation in a distributed setting, I don't see the benefit for this ...
Also, what are the fundamental limitations/research problems of todays hardware that prevent us from building a 400G NIC? I cannot think of anything outside of PCI-e bus getting saturated. We already have 400G ports on switches ...