According to WD, the transition to PLC-based SSDs will be slower because the disks will need more advanced SSD controllers than what's currently available. The production of PLC NAND flash memory doesn't seem the bottleneck, the availability of affordable advanced SSD controllers is the issue.
In particular, PLC-based SSDs will require even more complex error code correction. These SSD controllers will need more processing power, and there will also be a greater need for additional redundancy.
"I expect that transition [from QLC to PLC] will be slower," said Siva Sivaram, Western Digital's technology and strategy chief, at Bank of America Merrill Lynch 2021 Global Technology Conference (via SeekingAlpha). "So maybe in the second half of this decade we are going to see some segments starting to get 5 bits per cell."WD does expect rapid adoption of QLC NAND flash memory over the next two years plus.
Via: Tom's Hardware