> It's interesting that modern android phones appear to be using ext4 over hardware remapping layers too
File systems for block devices is a proven technology and is very mature. FTL firmwares and techniques is a widely known and proven technology, also.. since it has been a basic requirement for generations of consumer flash devices in order to be compatible with Windows.
So I am guessing that phone manufacturers, which are mostly integrators and not developers, are more interested in getting products out the door rather then working with chipset manufacturers to develop interfaces for theoretical large file system design.
So while I doubt having multiple layers of abstraction been the kernel and the storage device is optimal performance and reliability wise, it is certainly the most cost effective approach for today's consumer electronics.