10GbE has awful overhead if you use a network file system, and iSCSI is tricky to set up and is a dog unless you get a converged NIC with offload everything (there's a reason why single port Intel X5nn cards are often north of $300).
And T-Bolt 4 is the light at the end of the tunnel - and the tunnel still looks to be a couple of years long. https://forums.macrumors.com/threads/any-indication-or-hints-of-thunderbolt-4-80gbps.2018706/
Thunderbolt 4 possibly by next year then (2019), seems feasible then?
Not sure what you mean by network file system, but I'm thinking more on the lines for creatives who need fast desk speeds and large storage arrays, like video editors such as myself. You can already get 4 x NVME drives and PCIe switches that can run upwards of 40000 MB/s, so I can see these would fit in well to external exclosures, as well as those that still need even larger disk arrays, you already have Thunderbolt 3 that can handle most tasks.
I know nothing of the needs of data/science/programmer types that need everything to be hooked up to network file systems.