Hardware costs won't increase, you are right. But the costs to redesign the software to use an extra caching layer are going to be significant. Also, the current situation with flash memory being expensive won't last long, and moving to pure solid-state storage is still better than this 3-tier architecture. So, it's a large investment into a solution with only a couple years of lifespan.<p>Of course, this is probably wrong, and there is a startup somewhere doing just this, and they will be rich :)