I imagine a "live usb key"-on-ssd approach might work. Squashfs image of the OS, initrd script to preload all of that into ram at startup, in one sequential chunk and not in random order. Optional "persistence" mode, where saved files, changed settings, etc get added to a ext4/btrfs/f2fs partition.. The latter will of course slow you back to traditional ssd level of runtime performance..
I'm more annoyed with applications today than operating systems. On your regular sd card or usb flash, the amount of I/O that, for example, clicking back in firefox causes is about 2 seconds of I/O busy... Why? Because databases. Everything is a database these days, and databases go to great lengths to ensure that data is on disk NOW, RIGHTAWAY, and that data is written so that no corruption or loss occurs if power is lost or drive yanked in the middle of that write. This is the perfect recipie to defeat every I/O reducing, optimizing and make-go-faster algorithms that operating systems have.
Some people might care if a website cookie was lost, or that the visited/not-visited status of a link is comitted to disk within 1ms of you clicking the link.. Personally I'm not that fussy. Sometimes when running from usb live keys, I just copy and symlink the dot-mozilla directory to tmpfs (ramdisk) before starting firefox, and copy it back once I exit firefox. That means I avoid sqlite's disk-abusing tendencies, but with the risk that the entire browser session's history, cookies and saved forms/passwords data is lost to the state it was in before starting firefox.
I have a feeling there should be some middle ground between the default extreme, and my hacked together extreme.
People tell me windows has largely started to ignore requests made by apps wanting to commit data to disk immediately.. I guess they must have a new api for things that /really/ do want/need it.. Soon enough every app catches on to the new way of doing things, and we're back at slow I/O, and have to ignore requests through the new API, and create a new new API for things that really really want it. Sigh.