I can see you didn't spend much time with early SSDs back in the bad old days when 2.5" SSDs were unsophisticated and were essentially using the same architecture you'd find inside a $5 SD card from Walgreen's. Those SSDs often performed worse than uncached HDD's when you threw random writes at them.
Hu? What kind of applications do you write where 10 ms is too much latency?!
10ms per write is huge. Keep in mind that even a tiny 1KB database insert/update will involve multiple writes: the filesystem journal, the database journal, and the data itself. 10ms for each of those steps adds up quickly.
Alternately, consider writing a modestly-sized file to disk, like a 5MB mp3 file. You're spanning multiple flash cells (probably 40 128kb cells at a bare minimum, plus filesystem journaling etc) at that point. Now you're close to half a second of total latency. Oh, you're writing an album's worth of .mp3 files? We're up to five seconds of latency now. But probably more like ten seconds, if your computer is doing anything else whatsoever that involves disk writes in the background.
Why would you want to order the write of every 128 kB chunk of your MP3 album with regard to every other? A rotating HDD also has a latency of around 10 ms, and you certainly can write an album's worth of MP3 files faster than in 10 seconds - unless you insist on flushing every 128 kB chunk to the medium separately for no apparent reason, of course.
That you need multiple serialized writes for a commit is a valid point, but I would think that for most applications even a write transaction latency of 100 ms isn't a problem. Also, if you overwrite contents of an existing file without changing its size, you don't need any FS journaling at all, as the FS only needs to maintain metadata consistency, it's not a file-content transaction layer (details depend on the FS, obviously).
Cheap SD cards aren't slow because they have a 10 ms write latency, but because they have a very low IOP rate, which you also could not change by adding a cache and a buffer capacitor, but only by parallelizing writes to flash cells.
