Will most 3D NAND flash products continue to feature TLC?

For now, I expect almost all 3D NAND flash to be based on triple-level cell (TLC) flash. There are a number of reasons for this, but most of them boil down to vendor goals and available technology.

Flash storage is known for being much faster than rotational media storage, but suffers from capacity limitations. Because there is a limit to the number of memory cells that can be placed on a flash memory die, this impacts the overall storage capacity of a device.

Flash vendors have used two separate techniques to increase capacity: 3D NAND flash and the use of triple-level cells. The 3D NAND flash format is based on the idea that memory cells can be stacked vertically. This allows flash device capacity to be increased exponentially without the manufacturer having to increase the size of the die.

TLC flash increases capacity by storing an extra data bit in each cell. Single-level cell flash stores one data bit per cell, while multi-level cell flash stores two data bits per cell. TLC flash can store three bits per cell.

If a storage vendor's main goal is to increase the capacity of its flash storage, thereby driving down the cost per gigabyte, it makes sense to leverage both TLC flash and 3D NAND flash. Using the two technologies together allows flash capacity to be increased beyond what would be possible using one or the other.

Even though flash vendors are currently going with TLC flash in their 3D NAND products, that won't remain the case forever. Technology changes over time and eventually someone will develop a new type of cell that renders TLC obsolete. Until then, I expect 3D NAND flash products to make use of TLC flash.