I wonder if SSDs will ever gain an additional level of hierarchy, such as an NVRAM layer over the flash layer. "Hot write" zones could then live in the NVRAM layer and only be committed to flash infrequently. By "hot write," I'm thinking of stuff such as the journal on a journaled filesystem.
Aggressive use of TRIM when committing entries out of the journal would make it easier to reap blocks within this faster level of hierarchy, and would make the drive less sensitive to the size of the journal. That is, the journal could be much larger than the NVRAM size, but you'd still get the benefit if the *active* part of the journal fit in the NVRAM.
Having such a buffer should also make it much easier to wear-level the drive, pushing writes out of the NVRAM LRU only as needed, rotating among all the pieces of flash. The NVRAM would also allow the SSD to buffer requests (and mark writes as complete!) while it's in the middle of erasing sectors in the flash.
Sure, it'd be expensive, but I imagine it'd fly like a bat outta hell.