My point was more that the SSD will likely have lower latency than an Ethernet link in any case, as you've got the extra delay of data having to traverse both the local and remote network stack, as well as any switches that may be in the way. Additionally, in order to deal with that bandwidth you'll need to kit out not only the local machine, but also the remote one with expensive 400GbE hardware+transceivers, plus switches, and in order to actually store something the remote machine will also have to have either a ludicrous amount of RAM (resulting in a setup which is vastly more complex and expensive than the original RAIDed SSDs while offering presumably similar performance) or RAIDed SSD storage (which would put us right back at square one, but with extra latency). Maybe there's something I'm missing here, but I fail to see how this could possibly be set up in a way which outperforms locally attached swap space.

Yeah, but the point of RAM is fast random (the R in RAM) access times. There are ways to make slower memory work better for this by predicting what will be needed (grab a chunk of memory because accesses will probably need things with closer locality than pure random), but it can't be fixed. Cloud memory is good for non-random storage or storage that isn't time critical.