Dedicated pagefile.sys paging and/or ReadyBoost SSD drives.
Think about it. If someone built a modern SSD with say 4 – 12GB specifically designed for very high random 4K read/writes on a SATA III(II) interface they would make excellent little add-ons for most any desktop out there.
Older drives that could serve that purpose do exist, but 1) they generally are of an older, slower generation and 2) they do not market them for that purpose.
Buying a new desktop computer is something expensive that people put off for many years at a time. Buying an “add-on” for US$30-40 that speeds up their computer is something most any layman can get behind and be persuaded to do.
Note: A dedicated paging drive could in fact consist of a block of a few GB of DDR5 memory and a tiny SSD or CMOS to hold basic file structure so as to be multi-os compatible. Generally you want paging data to be wiped on shutdown/reboot anyway as well as being fast as possible. This gives us both those criteria. It does however completely confound and confuse all those layman out there that couldn’t figure out the difference between RAM memory and a hard drive up till now. (Laughs at the embarrassed tech geeks the first time a layman corrects them that their paging hard drive actually is “memory”.)
