|There have been a few products already mixing an SSD with a HDD to allow oft-used data to be quickly read and written while rarely used bulk data that get's streamed (rather than random access) e.g. video is relegated to the HDD. Why not do the same with two grades of NAND? A few GB of SLC (or MLC) for OS files and frequently accessed and rewritten program files, and several hundred GB of TCL (or QLC, etc) for less frequently written data that it is still desirable to access quickly (e.g. game textures & FMVs). Faster than a HDD hybrid, cheaper than an all-SLC/MLC design, and just as fast in the vast majority of consumer use cases (exceptions including non-linear video editing, large-array data processing).|
Of course SanDisk already does this in their AFM. They can configure some of the memory to be SLC and use it as a cache, thereby increasing both the external performance and the reliability versus pure MLC or TLC.