I'm not sure it's an order of magnitude reduction in real flash writes, but there have been some pretty promising results from experiments with collapsing those

I'm not sure it's an order of magnitude reduction in real flash writes, but there have been some pretty promising results from experiments with collapsing those three layers. Moving it all to the SSD gets you a Key-Value SSD, and moving it all to the host system gets you a Zoned SSD. Both ideas have seen enough interest from storage vendors and hyperscale cloud to end up standardized. So at this point it's mostly a matter of getting support added to common software like Postgres so that it's easy for smaller operations to adopt.