I've just bought a Pi4, 7" touchscreen and a case that takes the lot. I have converted the thing to boot and run off a USB3 stick and it runs rather faster than off the SD card. I'm not too bothered about trying to turn it into a NUC.
Nowadays I see a Pi as a kiosk style machine with extras. It is what it is. It is a fantastic jack of all trades. You get loads of GPIO of all sorts, bluetooth, wifi, ethernet, USB2 and 3, a quad core CPU and 2-8GB RAM. Two HDMI ports and a GPU. It's too much for jobs that you would deploy an ESP8266 or ESP32 and it's not enough for a full on desktop replacement.
I can't see a need for more than 16 or 32GB of storage on one of these things. If your use case needs greater storage then it probably needs more "box" or I simply lack imagination.
I have a C-64 under the telly in the sitting room (it has a QSII joystick and a USB interface). I have a ZX81 with 3" of rather stiff Blutac holding the 16Kb RAM expansion steady and a keyboard on a ribbon. Sometimes I go back to school and type in definitions for 8x8 blocks and make them run around the screen. I do not own a Sinclair C5, that would be silly.
It's terrible that 2-8GB RAM is not enough for a full on desktop replacement. You could run Windows 95 in 4 MB. Was that not a desktop? The original Mac was just 128 KB.
Suppose it was all for graphics. Scaling up for modern color depth and screen size, we should need about 400 MB for the Windows 95 level of efficiency, or about 64 MB for Mac level of efficiency. That's a huge overestimate because RAM is not all consumed by graphics.
In other words, modern software can't run a desktop properly without even 10 to 100 times as much RAM as it ought to need.
My desktop with KDE Plasma 5 consumes somewhere in the ballpark of 500 MB RAM initially on startup.
RAM consumption by Konsole, tmux, and Neovim (30+ loaded buffers) combined is negligible to say the least.
RAM consumption by my browser with 10+ windows and 100+ tabs loaded easily exceeds 4+ GB even when exclusively visiting supposedly "lightweight" text based sites (ie documentation).
Going beyond RAM, playing a video on YouTube occupies a small but noticeable fraction of total CPU time. A single script heavy ad laden site sometimes manages to occupy a problematically large fraction of all available cores. Depending on the site, Dark Reader might slow this all to a crawl for 10+ seconds as the bloated page gradually loads (I'm looking at you, Amazon).
A file server is a pretty basic task, and zfs is a pretty good choice of fs for a file server, and zfs wants all the ram you can scrape up.
But still there may not be many such examples so your point is still valid.
I use a 3b+ for a 3d printer and that means, octoprint, klipper, octolapse, live streaming from a webcam while printing, a web server and web ui with various plugins, a slicer (I don't slice on the pi, but it's there and I could) and for all that the 3b+ is hardly scratched while running full out. It's a 4g model that is always using only couple hundred meg if you don't count disk cache. This is exactly consistent with your supposition.
I can't see a need for more than 16 or 32GB of storage
on one of these things. If your use case needs
greater storage then it probably needs more "box" or
I simply lack imagination.
Generally yeah. One possible (slightly contrived) exception that comes to mind could be using it as "dumb" volatile storage like Redis/memcached/etc.
I say "dumb" because if you are leaning into any of Redis' more advanced stuff (sorted sets, pub/sub, whatever else they've thrown in lately) I suspect CPU would tend to become a bottleneck rather quickly once you've got > 8GB of data.
There are a few, and they're not too bad, but it's still something that would be neatly solved with an option of a PCIe slot or even onboard eMMC like on the compute module (assuming the eMMC or built-in NVMe was much faster than the one on CM3+ and below).
I’m surprised there’s no Raspberry Pi case with a slot for a 2.5” drive and integrated USB 3.0 SATA controller.